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FRANKLIN  INSTITUTE  LIBRARY 

PHILADELPHIA 


CIass.<£.AZ.<£«.  Book/^  J?.<£\3.  Accession..iL^..<2.<2. 


Article  VI. — The  Secretary  shall  have  authority  to  loan  to  Members  and 
to  holders  of  second  class  stock,  any  work  belonging  to  the  second  class, 
subject  to  the  following  regulations  : 

Section  1. — No  individual  shall  be  permitted  to  have  more  than  two  books 
out  at  one  time,  without  a  written  permission,  signed  by  at  least  two  mem- 
bers of  the  Library  Committee  ;  nor  shall  a  book  be  kept  out  more  than 
two  weeks  ;  but  if  no  one  has  applied  for  it,  the  former  borrower  may 
renew  the  loan.  Should  any  person  have  applied  for  it,  the  latter  shall 
have  the  preference. 

Section  2. — A  fine  of  ten  cents  per  week  shall  be  exacted  for  the 
detention  of  a  book  beyond  the  limited  time  ;  and  if  a  book  be  not  returned 
within  three  months  it  shall  be  deemed  lost,  and  the  borrower  shall,  in 
addition  to  his  fines,  forfeit  its  value. 

Section  3. — Should  any  book  be  returned  injured,  the  borrower  shall  pay 
for  the  injury,  or  replace  the  book,  as  the  Library  Committee  may  direct; 
and  if  one  or  more  books,  belonging  to  a  set  or  sets,  be  lost,  the  borrower 
shall  replace  them  or  make  full  restitution. 

Article  VII. — Any  person  removing  from  the  Hall,  without  permission 
from  the  proper  authorities,  any  book,  newspaper,  or  other  property  in 
charge  of  the  Library  Committee,  shall  be  reported  to  the  Committee,  who 
may  inflict  any  fine  not  exceeding  twenty-five  dollars. 

Article  VIII. — No  member  or  holder  of  second  class  stock,  whose 
annual  contribution  for  the  current  year  shall  be  unpaid  or  who  is  in 
arrears  for  fines,  shall  be  entitled  to  the  privileges  of  the  Library  or  Read- 
ing Room. 

Article  IX. — If  any  member  or  holder  of  second  class  stock,  shall  refuse 
or  neglect  to  comply  with  the  foregoing  rules,  it  shall  be  the  duty  of  the 
Secretary  to  report  him  to  the  Committee  on  the  Library. 

Article  X. — Any  Member  or  holder  of  second  class  stock,  detected  in 
mutilating  the  newspapers  pamphlets  or  books  belonging  to  the  Institute, 
shall  be  deprived  of  his  right  of  membership,  and  the  name  of  the  offender 
shall  be  made  public 


w 


Digitized  by  the  Internet  Archive 
in  2015  • 


V 


https://archive.org/details/notesuponindigoOOhaye 


NOTES  UPON  INDIGO. 


BY 


JOHN  L.  HAYES, 


SECRETARY  OF  THE  NATIONAL  ASSOCIATION  OF  WOOL  MANUFACTURERS,  FELLOW 
OF  THE  AMERICAN  ACADEMY,  AND  CORRESPONDING  MEMBER  OF  THE 
ACADEMY  OF  NATURAL  SCIENCES  OF  PHILADELPHIA. 


from  "  %>\t  bulletin  of  %  |tational  ^unatmttoxi  of  Wool  Jpanufactitrers." 


H  BOSTON: 
PRESS  OF  JOHN  WILSON  AND  SON. 
1873. 


TP 


THE  GETTY  C£*. 
LIBRARY 


\ 


PART  I. 


NOTES   UPON  INDIGO. 


PART  I. 


A  publication  devoted  to  the  interests  of  the  woollen  manufact- 
ure, while  giving  due  prominence  to  its  first  raw  material, 
wool,  cannot  neglect  the  secondary  materials  which  enter  into 
finished  fabrics.  The  attractiveness  and  utility  of  the  largest 
class  of  these  fabrics  are  due  to  the  hue  given  themdby  the  dyer  ; 
and  of  all  the  coloring  materials  one  of  the  most  precious  is 
indigo.  In  former  times,  as  it  still  does  at  the  East,  it  occupied 
with  madder  the  place  of  one  of  the  two  most  important  of  all 
dyeing  materials.  Forced  of  late  years  to  give  way  to  the 
marvellous  products  of  modern  chemistry,  it  will  doubtless 
resume  its  place  under  the  influence  of  a  more  enlightened 
economy  and  a  more  subdued  taste.  To  contribute  to  the 
hastening  of  this  return  is  one  object  of  this  essay.  The  most 
usual  reproach  against  American  fabrics  is  the  want  of  stability 
in  our  dyes,  —  a  reproach  without  justice,  if  applied  to  American 
fabrics  alone  ;  for  the  cheapening  of  dyestuffs  is  practised  in  all 
the  so-called  manufacturing  nations,  and  is  contemned  alone  in 
the  East,  from  which  we  have  derived  our  arts,  and  by  the  people 
whom  we  despise  as  barbarous.  To  remove  this  reproach  from 
American  fabrics  would  be  worthy  of  no  little  temporary  sacrifice 
on  the  part  of  our  manufacturers. 

The  value  of  indigo  as  a  dyeing  material  is  due  to  the  great 
stability  of  the  blue  color,  and  the  derivatives  from  blue,  which 
it  gives  to  fabrics,  especially  of  wool  and  cotton.  It  is  not 
sufficient  that  a  dyed  fabric  should  preserve  its  color  when  sub- 


2  y-oo 


4 


NOTES  UPON  INDIGO. 


mitted  to  violent  tests,  as  when  acted  upon  by  vegetable  or 
mineral  acids  or  alkaline  or  soapy  baths:  the  only" stable  dyes 
are  those  which  resist  air  and  light,  the  two  destructive  agents 
of  vegetable  colors.  Indigo,  from  the  remarkable  manner  in 
which  its  color  becomes  fixed  upon  a  fabric,  to  be  hereafter 
explained,  possesses  properties  of  resistance  and  stability  in 
a  higher  degree  than  any  blue  dye.  And  when  we  consider 
that  this  blue  has  not  only  its  own  hue,  but  is  the  best  founda- 
tion for  blacks,  greens,  purples,  and  even  browns,  the  impor- 
tance of  these  properties  cannot  be  over-estimated.  Says  M. 
de  Kseppelin,  a  chemist  and  manufacturer  of  Mulhouse,  in  one 
of  a  series  of  articles  furnished  to  the  Annates  die  genie  Civil , 
1864:  "So  high  are  the  properties  6f  resistance  and  stability 
which  indigo  possesses,  that  it  is  perhaps  to  be  regretted  for  the 
art  of  the  dyer  and  manufacturer  of  printed  calicoes,  that  the  use 
of  indigo  becomes  more  and  more  rare,  and  that  the  recent  dis- 
coveries wlKBa  modern  science  has  placed  at  the  service  of 
industry  are  daily  eliminating  it  from  our  factories.  I  have 
observed  that  whenever  we  have  to  dye  stuffs  of  a  high  price,  it 
is  indigo  which  always  serves  as  a  base  for  the  foundation  of  all 
the  blue  colors,  or  of  those  which  are  derived  from  blue.  It 
is  the  same  for  the  fabrication  of  printed  tissues,  which  serve 
for  the  poorer  classes,  whose  colors  should  have  great  stability 
without  much  increase  of  cost.  But  of  late  years,  especially, 
we  find  a  tendency  to  employ  colors  of  little  stability,  and 
to  prefer  them,  even  in  the  class  of  fabrics  first  referred  to, 
to  those  which  are  more  fast,  on  account  of  their  vivacity 
and  freshness  of  tone.  It  is  this  tendency,  which  the  con- 
sumer partakes  of  even  while  complaining  of  it,  that  the  textile 
manufacturers  ought  to  seek  to  combat.  How  often  have  I 
heard  the  greatest  manufacturers  of  Alsace  deplore  the  obliga- 
tion which  they  felt  that  they  were  under  of  printing  their 
tissues  by  means  of  colors  so  fugacious  and  so  little  resistant 
as  those  composed  from  aniline.  We  must  hope,  then,  in 
the  interest  of  that  industry,  that  while  adopting  the  marvellous 
discoveries  which  science  is  every  day  making,  there  shall  be 
made  a  less  general  application  of  them,  and  that  we  shall 


NOTES  UPON  INDIGO. 


5 


return  to  the  fabrication  of  the  styles  which  necessitate  the 
more  constant  employment  of  coloring  materials,  — less  brilliant, 
it  is  true,  but  more  adherent  to  the  tissues,  and  less  alterable  by 
air  and  light.  It  seems  to  me,  also,  that  taste  would  lose  noth- 
ing;  and  that  printed  stuffs,  colored  in  a  manner  less  brilliant, 
but  more  harmonious,  would  be  perhaps  more  appreciated,  espe- 
cially by  those  who  use  them." 

The  tendency  to  substitute  the  brilliant  for  the  stable  dyes 
prevails  too  much  in  our  own  manufacture.  A  very  considera- 
ble cloth  manufacturer  replied  to  our  inquiry  as  to  the  extent  to 
which  he  used  indigo  :  "  I  hardly  use  it  at  all  ;  the  dye  of  the 
indigo  blue  is  not  bright  enough  to  be  popular."  On  the  other 
hand,  we  have  heard  our  leading  manufacturer  of  carpets,  whose 
cultivated  taste  has  led  him  to  partake  of  M.  de  Kasppelin's 
views,  deplore  the  introduction  of  aniline  dyes,  as  a  positive 
calamity  to  the  textile  industry.  It  is  the  influence  of  the 
trade,  the  immediate  consumers  of  fabrics,  rather  thari^the  judg- 
ment of  manufacturers,  which  promotes  the  use  of  the  modern 
fugacious  dyes.  The  dealers  desire  not  only  to  imitate  the 
fashionable  colors  of  European  goods,  but  to  secure  the  utmost 
cheapness.  One  of  our  largest  manufacturers  of  woollen  goods, 
who  had  made  a  special  study  of  the  best  processes  abroad,  and 
was  desirous  of  bringing  better  dyed  goods  into  more  gen- 
eral consumption,  urged  one  of  his  largest  customers,  an  exten- 
sive dealer,  to  allow  him  to  dye  the  waterproof  cloakings  which 
he  was  furnishing  for  his  house,  in  fast  indigo  colors,  assuring 
him  that  he  would  charge  simply  the  additional  cost  of  the 
indigo,  without  profit.  The  offer,  which  involved  the  cost  of  only 
a  few  cents  a  yard,  which  would  have  been  gladly  paid  by  the 
last  consumer  if  the  difference  of  value  had  been  made  known, 
was  declined.  It  is  not  improbable  that  the  inferior  goods  which 
the  manufacturer  was  compelled  to  furnish  were  sold  to  the 
public  as  fast  dyed.  Our  manufacturers,  therefore,  may  not 
have  been  responsible  for  the  predicament  in  which  the  most 
enthusiastic  defender  of  our  protective  policy  found  himself,  as 
we  have  it  from  his  own  lips.  Being  about  to  make  a  speech  in 
Congress  in  defence  of  American  industries,  he  put  on,  for  the 


6 


NOTES  UPON  INDIGO. 


first  time,  a  coat  declared  to  have  been  made  of  American  cloth. 
Sitting  down,  heated  and  perspiring  from  the  excitement  of  his 
effort,  he  found  that  beneath  the  arms  whose  gestures  had  en- 
forced his  eulogies  of  American  industry,  the  pretended  fast 
blue  of  his  coat  had  become  red,  literally  blushing  for  its  un- 
merited praise.  That  fast-dyed  goods  of  the  highest  excellence 
can  be  and  are  furnished  by  American  manufacturers,  is  shown  by 
our  army  cloths.  The  government  specifications,  copies  of  which 
are  published  elsewhere  in  this  number,  require  that  all  the  blue 
woollen  cloth,  cap  cloth,  and  flannels  furnished  for  the  army  shall 
be  "pure  indigo  dyed."  The  requisition  is  strictly  enforced. 
The  admirable  effect  of  this  regulation  may  be  witnessed  at  any 
dress  parade  of  a  battalion  of  United  States  soldiers.  The 
persistency  and  uniformity  of  the  hue  under  constant  wear  — 
the  cloth  of  the  common  soldier  in  its  superior  dye  often  favor- 
ably contrasting  with  the  finer  but  fancy  dyed  cloth  of  the 
officer  —  is  one  of  the  circumstances  which  justify  the  assertion, 
that  our  army  is  the  best  clothed  in  the  world.  The  contrast  is 
more  remarkable  still  with  the  quondam  blue  cloth,  converted 
by  sun  and  rain  into  every  shade  of  shabbiness,  which  we  pur- 
chased in  Europe  for  our  soldiers  at  the  commencement  of  our 
late  war. 

ORIGIN  AND  EXTRACTION  OF  INDIGO. 

Indigo  is  a  coloring  material  of  vegetable  origin,  which  owes 
its  color  and  its  important  applications  to  a  direct  blue  principle, 
known  under  the  name  of  indigotine.  It  has  been  used  as  a 
dyestuff  from  time  immemorial,  by  the  inhabitants  of  India ; 
and  it  is  from  the  East,  the  cradle  of  the  textile  arts,  that  Eu- 
rope has  derived  it.  It  was  probably  received  from  India  by  the 
Greeks,  among  other  products  first  made  known  to  them  by  the 
expeditions  of  Alexander  the  Great.  Dioscorides  clearly  refers 
to  indigo  in  mentioning  the  two  coloring  matters  brought  from 
India.  Pliny  mentions  a  coloring  material,  having  an  admirable 
mixture  of  blue  and  purple,  as  coming  from  India,  which  he  calls 
indicum.  That  he  refers  to  indigo  is  curiously  manifest  by  the 
test  which  he  gives,  by  which  the  genuine  drug  might  always  and 


NOTES  UPON  INDTGO. 


7 


certainly  be  distinguished  from  the  spurious.  This  is  by  put- 
ting it  on  live  coals,  when,  says  he,  "  the  true  indicum  will  burn 
with  a  flame  of  a  most  beautiful  purple  tint."  The  purple 
vapor  from  burning  indigo  is  still  a  characteristic  test.  The 
Romans,  it  is  apparent,  used  indigo  only  as  a  pigment,  not 
knowing  what  is  still  the  most  important  art  connected  with  its 
use,  —  how  to  make  it  soluble  so  as  to  be  available  in  dyeing. 

That  indigo  as  a  commercial  product  was  first  obtained  from 
India  is  not  only  proved  by  the  testimony  of  Pliny,  and  other 
ancient  writers,  but  is  confirmed  by  a  variety  of  circumstances, 
and  particularly  by  its  name,  which  is  known  to  have  been  nil 
in  the  Hindu  language,  from  the  earliest  times  of  which  there  is 
mention  of  it.  This  name  is  still  given  by  the  Hindoos  to  the 
color  blue,  and  to  all  the  plants  producing  indigo.  The  Arabs 
and  Egyptians,  who  obtained  a  knowledge  of  indigo  from  India, 
adopted  the  Hindu  name,  the  Arabs  calling  it  nil  or  nir,  and  the 
Egyptians  nil  or  nieL  The  Portuguese  preserved  the  Indian 
name,  with  a  slight  modification,  the  substance  being  called 
aniliera  in  their  language.  The  coloring  substances  after- 
wards found  in  coal-tar  having  been  first  found  in  indigo,  mod- 
ern science  has  adopted  for  them  the  name  of  aniline. 

It  has  been  asserted  that  this  substance  was  not  known  in 
Europe  until  the  time  of  the  discovery  of  the  passage  to  India 
round  the  Cape  of  Good  Hope.  But  Dr.  Bancroft  has  shown 
that  indigo  was  brought  by  merchants  from  India  to  Alexandria, 
and  thence  to  Venice,  when  that  city  was  the  entrepot  of  Europe 
and  the  East.  It  doubtless  contributed  to  the  excellence  which 
the  Italian  states  .first  attained  in  the  wool  manufacture.  The 
drug  was  called  endigo  in  Venice,  and  it  is  from  that  city  that 
we  have  derived  its  name  and  use.  It  was  imperfectly  known  in 
England  under  its  Spanish  name  in  the  sixteenth  century,  for 
we  find  in  Hackluyt  w  Voyages  "  his  instructions  to  a  traveller 
who  was  going  to  Turkey  to  ascertain  "  if  anile ,  that  coloureth 
blue,  be  a  natural  commodity  of  those  parts,  and  if  it  be  com- 
posed of  an  herbe." 

The  general  introduction  of  indigo  into  Europe  was  impeded 
by  legislative  enactments,  prompted  mainly  by  those  employed 


8 


NOTES  UPON  INDIGO. 


in  industries  which  it  threatened  to  displace.  These  were  chiefly 
the  producers  of  and  dealers  in  woad,  formerly  used  exclusively 
for  dyeing  blue,  and  the  corporation  of  woad  dyers.  When 
dyers  from  Italy  and  Flanders  attempted  to  introduce  the  supe- 
rior dyes  of  indigo,  the  woad  interests  were  sufficiently  powerful 
to  induce  the  Elector  of  Saxony  to  denounce  the  use  of  the  new 
dyestuflf.  It  was  pronounced  in  the  Diet  of  the  Empire  as  "  a 
corrosive  color/'  and  "fit  food  only  for  the  devil, " fressende  teu- 
feh.  Similar  propositions  were  made  in  England  and  France, 
in  which  latter  the  free  use  of  indigo  was  not  permitted  until 
1737. 

Although  indigo  as  known  in  the  arts  is  a  product  of  vegetable 
origin,  we  must  not  omit  to  notice  that  one  source  of  its  produc- 
tion is  the  human  body.  It  was  discovered  some  years  since 
that  the  blue  color  sometimes  found  in  diseased  urines,  and  in 
certain  suppurations,  is  due  to  indigo.  Dr.  Schunck,  in  some 
papers  read  before  the  Royal  Society,  has  shown  that  it  is  a  fre- 
quent constituent  of  urine  secreted  by  persons  in  a  healthy  state, 
and  that,  in  fact,  it  is  produced  generally  when  persons  do  not 
take  sufficient  exercise  ;  and  he  has  several  times  succeeded  in 
producing  it  by  taking  in  his  food  a  rather  large  excess  of  sugar. 
He  has  found  this  substance  also  in  the  urine  of  beef  cattle.  It 
must  also  be  observed  that  the  chemical  actions  of  indigotine 
wTith  oxidizing  agents,  showing  indigo  to  have  a  very  close 
relation  to  aniline  and  carbolic  acid,  both  products  derived  from 
coal-tar,  have  produced  in  the  minds  of  chemists  the  conviction 
that  indigotine,  like  alizarine,  the  coloring  principle  of  madder, 
will  one  day  be  artificially  produced  from  coal-tar. 

The  plants  which  are  known  to  furnish  indigo  are  quite  numer- 
ous, being  not  less  than  sixty  ;  they  do  not  all  belong  to  the 
same  family,  and  none  of  them  contain  the  coloring  principle 
already  formed.  The  most  important  belong  to  the  leguminous 
family,  from  which  most  of  the  vegetable  dyes  are  derived,  and 
to  the  genus  indigofera.  The  species  cultivated  and  most 
esteemed  are  Indigofera  tinctoria,  I.  disperma,  I.  anil,  I. 
argentea. 


NOTES  UPON  INDIGO. 


9 


The  principal  source  of  the  indigo  of  commerce  is  the  Indigo- 
fera  tinctoria.  The  accompanying  figure  is  a  correct  represen- 
tation of  the  plant,  and  we  may  dispense  with  a  description  of 
its  botanical  characters,  observing  only  that  the  plant  has  a  half 
woody  stem,  and  rises  to  the  height  of  from  three  to  five 
feet.  The  plants  exhale  a  strong  odor  towards  evening  in  the 
fields  where  they  are  cultivated.  The  leaves  have  a  disagree- 
able taste,  and  rapidly  putrefy  in  water.  The  plant  originated  in 
Campaja,  or  Guzerat,  but  is  cultivated  in  Hindostan,  China, 
Java,  and  in  the  East  Indies  generally.  It  was  carried  by  the 
Spaniards  to  South  America  and  the  West  Indies,  and  it  can 
be  acclimated  in  all  hot  countries.  The  Indigo  fera  ar gen-tea, 
or  indigo-plant  of  Egypt,  furnishes  the  indigo  produced  in  that 
country  and  Arabia. 

The  culture  of  the  plant  and  the  production  of  commercial 
indigo  is  carried  on  on  a  vast  scale  in  Lower  Bengal.  We  have 
before  us  a  large  map,  placed  at  our  disposal  by  an  India  mer- 
chant of  Boston,  showing  the  location  of  each  of  the  hundreds  of 
factories  of  that  important  centre  of  production.  These  facto- 
ries have  been  developed  by  British  enterprise ;  and  India  thus 
receives  some  slight  compensation  for  the  ruin  of  her  cotton 
manufacture  by  the  same  influence. 

The  propagation  of  the  indigo-plant  in  that  country  is  made 
by  sowing  in  a  thoroughly  tilled  silico-argillaceous  soil.  The 
seed  of  the  plant  is  sowed  annually  in  the  spring  or  autumn, 

2 


10 


NOTES  UPON  INDIGO. 


according  to  the  variety  used,  some  germinating  more  slowly, 
and  requiring  to  remain  in  the  ground  longer  than  others.  The 
time  of  putting  in  the  seed  is  also  governed  by  the  nature  of  the 
soil  and  its  position  in  respect  to  neighboring  rivers.  In  the 
lowlands  subject  to  inundations,  the  indigo  ought  to  be  all 
cut  at  the  period  of  the  rains  and  inundations,  which  would  de- 
stroy the  crop  in  a  brief  time.  Besides,  during  the  rainy  period 
the  planter  has  at  his  disposal  sufficient  water  to  commence 
his  operations  of  fabricating  the  indigo,  which  is  the  suitable^ 
time  for  beginning  the  cutting  of  the  plant.  The  time  of 
cutting  the  indigo-plants  is  therefore  regulated  by  the  elevation 
of  the  land  and  danger  from  floods.  The  high  lands  are  always 
sowed  several  weeks  after  those  subject  to  inundations. 

The  Chinese  prick  out  the  young  plants  in  parallel  rows, 
always  preserving  the  land  quite  clear  of  weeds.  By  taking 
away  the  blossoms  of  the  plant  before  their  development,  they 
increase  the  growth  of  the  leaves,  and,  consequently,  the  return 
.of  indigo  ;  for  it  is  in  the  leaves  principally  that  the  coloring 
material  is  found. 

In  certain  localities  the  planters  break  off  the  leaves  which 
have  acquired  a  bluish  green  tint.  But  more  frequently  the 
whole  plant  is  cut  down  close  to  the  ground  in  the  months  of 
June  or  July,  when  the  flowers  begin  to  open.  The  portion 
of  the  plant  which  remains  pushes  up  quite  rapidly,  and  fur- 
nishes a  second,  and  even  third,  and  sometimes,  though  rarely, 
a  fourth  cutting.  The  quality  of  the  product  diminishes  accord- 
ing to  the  number  of  the  cuttings. 

The  plant  called  nil9  cut  down  to  the  root  and  gathered  up 
in  packages,  is  worked  up  the  same  evening.  The  package  is 
formed  from  the  product  of  a  space  of  land  embraced  by  a  chain 
about  three  yards  long.  The  value  of  the  first  material  changes 
with  the  value  of  the  soil.  Thus,  one  soil  produces  a  plant 
which  has  many  stems  and  few  leaves,  while  another  gives  many 
leaves  and  few  stems.  The  richness  in  coloring  material  de- 
pends upon  the  quantity  of  leaves,  but  varies  also  with  an  equal 
weight  of  leaves  with  atmospheric  influences.  Thus  regular 
dealers  in  the  article  observe  a  marked  difference  in  the  quality 
of  indigo  in  different  seasons. 


NOTES  UPON  INDIGO. 


11 


M.  A.  Koechlin  Schwartz  has  recently  published  some  inter- 
esting notes  upon  the  preparation  of  indigo  in  Lower  Bengal. 
In  that  country,  which  furnishes  excellent  indigo,  the  factory 
includes,  besides  filters,  presses,  a  steam-engine,  drying  appa- 
ratus, and  reservoir  of  water,  two  lines  of  vats,  arranged  one 
above  the  other,  from  fifteen  to  twenty  in  each  line.  These  vats 
are  built  up  with  bricks,  and  covered  with  a  strong  coat  of  solid 
and  well  made  stucco.  They  are  square,  about  six  yards  on  a 
side,  and  about  a  yard  deep.  The  back  row  is  about  a  yard 
above  the  front  one.  The  plant  is  fermented  in  the  vats  of  the 
upper  row  ;  when  the  operation  of  fermentation  is  terminated,  a 
faucet  is  opened,  and  the  liquid  is  run  into  the  lower  vat.  The 
water  of  the  Ganges,  which  is  relatively  pure,  and  thus  well 
suited  for  this  work,  is  brought  into  basins  of  deposition,  where 
it  becomes  clarified,  and  is  distributed  by  a  common  canal  to  the 
vats  of  the  upper  row.  The  plants,  cut  in  the  morning  and 
bound  up  into  packages,  come  to  the  factory  after  midday,  and 
are  thrown  into  the  vat  in  the  evening.  A  vat  contains  one 
hundred  packages  carefully  arranged,  one  beside  the  other  ;  heavy 
timbers  are  placed  upon  the  plants,  which  are  pressed  down  by 
means  of  large  wedges.  It  is  necessary  that  the  plants  should 
be  pressed  together  very  compactly,  as  without  this  the  fermen- 
tation does  not  take  place  to  advantage.  At  nightfall  the 
water  is  introduced  into  the  vats,  and  fills  them  so  as  completely 
to  submerge  the  plants.  The  fermentation  is  more  or  less  pro- 
longed according  to  the  temperature.  Its  duration  varies  from 
nine  to  fourteen  hours.  The  workmen  judge  as  to  the  pro- 
cedure of  the  operation  by  withdrawing  a  little  of  the  liquid 
in  the  lower  vat.  If  it  is  of  a  clear  pale  yellow  when  with- 
drawn, it  will  furnish  a  product  less  abundant  but  more  pure 
than  if  of  a  deep  gold  color. 

At  the  moment  of  its  issue  from  the  fermenting  vat  the  liquid 
is  of  a  yellow  color,  more  or  less  deep.  The  liquid  is  allowed 
to  remain  undisturbed  for  a  brief  period,  when  twelve  naked 
men,  armed  with  long  bamboos,  enter  the  vat  to  beat  the  water 
while  it  is  still  warm.  During  this  time  the  upper  vat  is  emptied 
and  cleaned  out  for  the  succeeding  operation.    One  vat  requires 


12 


NOTES  UPON  INDIGO. 


seventeen  workpeople  (twelve  men  and  five  women).  They 
thrash  the  water  for  two  or  three  hours.  The  liquid  passes  by 
little  and  little  to  a  pale  green,  and  the  indigo  is  found  on  suspen- 
sion in  the  form  of  small  floccules.  The  liquor  is  suffered  to  re- 
main undisturbed  for  half  an  hour  ;  it  is  then  gradually  decanted 
by  opening,  one  after  the  other,  the  discharging  holes  placed  at 
different  heights.  The  water  returns  to  the  river,  and  the  pre- 
cipitate, under  the  form  of  a  thin  bouille,  is  turned  into  a  reser- 
voir. This  bouille  is  pumped  up  into  a  vessel,  and  made  to  boil 
for  a  moment  to  prevent  a  second  fermentation,  which  would 
injure  the  quality  of  the  product,  by  turning  it  black.  It  is 
suffered  to  rest  about  twenty  hours,  and  the  next  morning  it  is 
again  subjected  to  boiling,  the  ebullition  being  kept  up  three  or 
four  hours.  The  boiling  deposit  is  then  turned  off  upon  a  large 
filter,  through  which  the  water  drips.  This  filter  is  composed 
of  a  vat  constructed  of  masonry,  covered  with  stucco,  about 
eighteen  feet  long  by  six  feet  wide  and  three  feet  deep.  This 
is  covered  with  bamboos,  upon  which  is  a  grating  of  smaller 
reeds,  and  above  by  a  stout  strained  cloth.  There  remains 
upon  the  cloth  a  thick  paste,  of  a  deep  blue  and  nearly  black 
color.  The  water  which  is  run  into  the  vat  deposits  some  indigo 
which  has  pressed  through  the  filter.  This  is  decanted  after 
being  allowed  to  rest,  and  the  turbid  liquid  is  boiled  the  next 
day  with  the  fresh  indigo. 

The  paste  of  the  filter  is  introduced  into  some  small  boxes  of 
wood,  pierced  with  holes,  and  provided  above  and  below  with  a 
strong  cotton  cloth.  The  whole  is  again  covered  with  a  piece 
of  stuff,  and  then  with  a  covering  of  wood,  pierced  with  small 
holes,  and  it  is  placed  under  a  press,  the  force  being  gradually 
applied,  so  as  to  cause  the  water  to  run  out  as  much  as  possible. 
There  is  withdrawn  from  the  box  a  cake  of  the  size  of  a  cake  of 
Marseilles  soap.  The  water  squeezed  out  flows  back  into  the  fil- 
tering vat,  to  be  boiled  again  with  the  fresh  indigo.  The  drying 
of  the  cakes  ought  to  be  done  very  slowly. 

The  dry-house  is  a  large  building  of  masonry,  quite  high,  and 
pierced  with  many  openings,  provided  with  narrow  blinds,  to 
prevent  the  direct  light  of  the  sun  from  penetrating  into  the  in- 


NOTES  UPON  INDIGO. 


13 


terior.  Cure  is  taken  also  to  surround  the  dry-house  with  large 
shade-trees.  The  cakes  take  from  three  to  four  days  to  dry, 
after  which  they  are  packed  in  small  boxes  and  carried  to  Cal- 
cutta, the  great  market  of  Bengal. 

The  details  above  given  apply  to  the  factories  managed  by 
European  planters.  The  natives  operate  in  nearly  the  same  manner, 
but  with  less  care,  and  consequently  their  products  are  inferior. 
The  average  product  of  indigo  in  Lower  Bengal  is  stated  at 
4,000,000  kilograms,  or  8,840,000  pounds  per  year.  The  most 
remarkable  fact  to  be  noticed  in  these  operations  is,  that  the  blue 
principle  is  developed  by  chemical  action  from  certain  absolutely 
colorless  principles  existing  in  the  plant.  The  theory  of  the 
change  effected  is  still  somewhat  in  doubt,  because  no  chemist  has 
studied  the  fresh  plant,  and  observed  upon  the  spot  the  phases  of 
the  operation  of  the  production  of  indigo  on  a  large  scale.  But 
the  most  accepted  theory  is  that  derived  from  the  researches  of 
Dr.  Schunck,  upon  the  isatis  or  woad-plant,  which  produces 
indigotine  in  a  much  less  degree  than  the  true  indigo-plants  ; 
viz.,  that  the  indigo  exists  in  the  plants  combined  with  sugar, 
forming  a  glucoside,  to  which  he  gives  the  name  indictm. 
This  compound,  under  the  influence  of  fermentation  in  the  man- 
ufacturing process,  is  supposed  to  be  unfolded  into  indigo  and 
sugar. 

Without  dwelling  upon  this  question,  which  is  beyond  our 
province,  we  observe  that  the  plants  of  the  genus  indigofera 
are  used  for  the  production  of  commercial  indigo,  on  account 
of  the  greater  richness  in  the  coloring  principle.  Other  plants, 
which  furnish  the  same  coloring  principle,  indigotine,  are  more 
frequently  used  directly  in  dyeing  to  furnish  the  blue  principle 
than  they  are  for  the  production  of  indigo. 

The  most  important  of  these  plants,  although  there  are  others, 
such  as  the  Polygonum  tinctorium  and  the  Nerium  tinctorium, 
is  the  Isatis  tinctoria,  which  produces  pastel,  or  woad.  This 
plant  belongs  to  the  family  Qf  crucifera3,  and  is  a  biennial.  It 
is  represented  in  the  accompanying  figure. 


NOTES  UPON  INDIGO. 


The  leaves  which  surround  the  stem  are  collected  in  May  or 
June  of  the  second  year,  when  they  begin  to  turn  yellow.  The 
wasted  and  dried  leaves  are  sometimes  used  directly  for  dyeing, 
but  more  generally  the  leaves,  after  being  cut  and  dried,  are 
carried  to  a  mill,  and  then  ground  to  a  paste,  after  which  it  is 
formed  into  a  mass  or  heap,  and  being  covered  to  protect  it  from 
rain,  is  left  to  undergo  a  partial  fermentation  for  about  a  fortnight. 
The  heap  is  then  well  mixed  and  formed  into  balls,  which  are 
exposed  to  the  sun  and  wind  to  dry,  and  thereby  prevent  the 
putrefaction  which  would  otherwise  take  place.  Being  afterwards 
collected  in  heaps,  these  balls  again  ferment,  become  hot,  and 
emit  the  odor  of  ammonia,  which  Hume  tells  us,  in  the  History  of 
England,  gave  such  offence  to  Queen  Elizabeth  that  she  issued 
an  edict  to  prohibit  the  cultivation  of  this  plant.  After  the  heat 
has  continued  for  some  time,  these  balls  fall  into  a  dry  powder, 
in  which  form  the  woad  is  usually  sold  to  the  dyer.  The  best 
French  woad  comes  from  Provence,  Languedoc,  and  Normandy. 
In  Germany,  the  pastel  of  Thuringia  is  used  almost  exclusively  ; 


NOTES  UPON  INDIGO. 


15 


the  packages  have  the  trade-mark  of  three  towers,  with  the  num- 
bers 4,  5.  In  this  country,  owing  probably  to  the  prejudices 
of  practical  dyers,  who  have  generally  come  from  England,  the 
Lancashire  woad  is  almost  exclusively  used.  The  very  little 
imported  of  late  years,  ranging  from  two  thousand  to  twelve 
thousand  dollars  annually  in  value,  is  used  for  mixing  with 
tindigo  in  the  so-called  woad  vat,  to  be  hereafter  described. 

COMMERCIAL  INDIGOES. 

The  following  description  of  the  indigoes  of  commerce  is  taken 
principally  from  Schutzenberger's  excellent  treatise  on  coloring 
materials.  It  coincides  very  nearly  with  that  given  by  Napier 
from  Dumas  and  Chevrueil.  Indigoes  are  classed,  according  to 
their  origin,  into  three  groups. 

1.  Indigoes  of  Asia  (from  Bengal,  Oude  or  Coromandel, 
Manilla,  Madras,  and  Java). 

2.  Indigoes  of  Africa  (Egypt,  Island  of  France,  Senegal). 

3.  Indigoes  of  America  (Guatemala,  Caraccas,  Mexico, 
Brazil,  and  the  West  Indies). 

The  three  varieties  in  most  esteem  are  those  of  Bengal,  Java, 
and  Guatemala. 

Indigoes  of  Java.  —  These  are  distinguished  by  the  great 
purity  of  their  coloring  material.  They  contain  the  minimum 
of  extractive  organic  matter.  If,  in  spite  of  this,  they  do  not 
give  a  high  yield  of  indigotine  ;  this  is  owing  to  a  mixture  of 
silicious  mineral  substances  with  their  paste.  The  paste  is  soft. 
It  adheres  strongly  to  the  tongue,  and  its  density  is  feeble. 
They  are  generally  of  a  pure  blue,  light  or  ash  colored  in  the 
kinds  which  are  less  rich,  and  of  a  magnificent  violet  blue  in  the 
superior  qualities.  The  last  take  a  beautiful  copper  color  when 
scratched  by  the  nail.  They  are  placed  in  the  very  first  rank 
among  all  indigoes  in  respect  to  fineness  and  beauty,  if  not  in 
richness  in  the  blue  coloring  principle.  Their  purity,  complete 
absence  from  carbonate  of  lime,  and  the  small  quantity  of 
foreign  organic  materials  which  they  contain,  cause  them  to  be 
much  sought  for,  for  the  preparation  of  carmine  of  indigo.  The 
consumption  of  the  Javan  indigoes  in  this  country  is  so  small  as 
not  to  be  appreciated. 


16 


NOTES  UPON  INDIGO. 


Bengal  Indigoes.  — These  are  the  indigoes  par  excellence, 
for  in  them  are  found  the  most  varied  qualities,  from  the  most 
beautiful  and  rich  to  the  most  ordinary.  The  superior  qualities 
are  of  a  deep  violet  blue,  with  a  fine  and  uniform  paste  ;  they 
adhere  to  the  tongue,  are  easily  pulverized,  and  take  a  beautiful 
coppery  tint  when  scratched  by /the  nail.  The  fresh  fracture 
shows  a  magnificent  purplish  blue  reflection.  Their  yield  in# 
indigotine  does  not  surpass  seventy-two  per  cent. 

After  these  come  the  reddish  violet  indigoes  with  a  purplish 
hue,  and  a  fracture  more  uniform  and  shiny.  They  are  also 
more  dense  and  hard  than  the  superior  qualities.  The  reddish 
hue  does  not  proceed  from  the  greater  or  less  amount  of  coloring 
material  contained,  but  from  the  presencp  of  a  greater  quantity 
of  brown  and  red  extractive  matter.  These  qualities  are  not  to 
be  despised,  for  the  kinds  which  give  the  best  results  in  the 
dyeing  vat  are  found  in  these  indigoes.  It  would  seem,  in  fact, 
says  the  author  whom  we  are  following,  "  that  the  browns  and 
reds  of  indigo  play  an  important  part  in  vat  dyeing,  that  they 
are  able  to  become  dissolved  and  to  fix  themselves  upon  the 
tissues  at  the  same  time  as  the  indigotine,  and  thus  operate  to 
reinforce  the  hue.  The  fact  is,#that  dyers  generally  prefer  the 
reddish  indigoes  to  the  other  varieties."  Among  the  Bengal 
indigoes  there  is  found  a  clear  blue  variety,  less  rich  in  coloring 
matter,  but  also  more  exempt  from  organic  substances.  The 
impurity  is  constituted  by  mineral  matters.  It  is  less  dense, 
adheres  strongly  to  the  tongue,  and  does  not  take  a  coppery  hue, 
like  the  other  varieties,  when  scratched  by  the  nail. 

The  worst  qualities  of  the  Bengal  indigoes,  as  in  all  the 
species,  are  the  clear  blues,  shading  on  to  gray  or  green.  This 
coloration  denotes  a  great  quantity  of  extractive  matter  different 
from  the  indigo  brown  which  characterizes  the  red  varieties,  and 
completely  inert.  These  indigoes  are  hard,  dense,  adhere  little 
or  none  to  the  tongue,  and  do  not  show  coppery  reflections  when 
scratched. 

The  most  skilful  connoisseurs  distinguish  forty-three  varieties 
of  Bengal  indigo.    The  most  important  are  the  following  :  — 
1.  Superfine  blue,  light  or  floating.  —  Color  bright  blue; 


NOTES  UPON  INDIGO. 


17 


light,  friable,  and  spongy  ;  adherent  to  the  tongue,  soft  to  the 
touch,  showing  coppery  reflections  when  rubbed  by  the  nail; 
paste  uniform  and  pure. 

2.  Fine  blue. — Like  the  preceding,  but  the  color  a  little 
less  vivid. 

3.  Violet  blue. — A  little  less  light  and  friable.  Has  a  violet 
blue. 

4.  Superfine  violet. 

5.  Superfine  purple. 

6.  Fine  violet. 

7.  Good  violet. 

8.  Red  violet. 

9.  Ordinary  violet. 

10.  Good  soft  red. 

11.  Good  red. 

12.  The  indigoes,  fine  coppery,  good  coppery,  ordinary  cop- 
pery, and  low  coppery. 

The  Indigoes  of  Oude  and  Coromandel.  —  These  are 
made  in  the  interior  of  Hindostan.  Those  of  the  best  quality 
correspond  to  the  middling  Bengal  indigoes,  and  are  met  with  in 
square  masses,  having  an  even  fracture,  but  are  more  difficult  to 
break  ;  the  inferior  qualities  are  heavy,  of  a  sandy  feel,  having 
a  blue  color,  bordering  on  green  or  gray,  or  even  black ;  often 
in  large  squares,  and  covered  with  a  slight  crust  or  rind  of  a 
greenish  color.  They  are  the  most  difficult  to  break  of  all  the 
indigoes  of  commerce. 

Madras  Indigoes. — They  have  a  grained  fracture,  and  are 
of  a  cubical  figure.  The  superior  qualities  have  no  rind.  The 
qualities  are  fine  blue,  mixed  violet  blue,  and  ordinary.  They 
are  all  lighter,  and  less  rich  in  coloring-matter  than  the  Bengal 
indigoes. 

Manilla  Indigoes.  —  These  occur  in  cubical  blocks,  flat 
squares,  or  in  irregular  pieces.  They  are  light,  with  a  fine 
paste,  and  of  a  clear  blue.  They  effervesce  with  acids,  showing 
the  presence  of  carbonate  of  lime  incorporated  in  their  paste. 
They  are  consequently  poor  in  coloring  material,  and  are  hence 
almost  exclusively  used  as  a  bluing  material  in  washing  fabrics. 

3 


18 


NOTES  UPON  INDIGO. 


American  Indigoes.  Guatemala,  —  These  indigoes  are  pro- 
duced now  altogether  in  Hunduras,  although  they  still  retain  in 
commerce  the  name  of  Guatemalan.  They  are  generally 
found  in  small  pieces,  irregular  in  form  and  size,  and  come  in 
envelopes  of  skin  containing  about  half  as  much  as  the  Bengal 
chests.  Putting  aside  the  difference  in  exterior  form,  these  indi- 
goes approach  very  closely  to  those  of  Bengal.  The  same 
qualities  are  found,  only  they  are  more  frequently  mixed.  The 
clear  blue  is  more  rare,  and,  when  it  is  found,  it  is  poorer  in  col- 
oring matter.  In  purchasing  these  indigoes  it  is  necessary  to 
beware  of  the  reds,  which  often  contain  a  strong  proportion 
of  the  brown  extractive  matter.  It  is  not  rare  to  find  among 
the  Guatemalan  indigoes  beautiful  specimens  of  the  blue  violet, 
equal  to  the  richest  Bengal  variety.  Unfortunately,  this  superior 
variety  is  generally  mixed  with  inferior  kinds,  as  to  have  less 
value.    The  American  indigoes  are  classified  as  follows  :  — 

Guatemala  for o. — Bright  blue,  paste  uniform,  soft  and 
light.  This  variety,  in  Bancroft's  time,  was  the  most  esteemed  of 
all  indigoes. 

Guatemala  sobr  e  salient  e.  — Less  light,  the  paste  firmer  and 
the  blue  less  beautiful. 

Guatemala  cortex  or  copper- colored, — Paste  less  firm  and 
heavier,  coppery  red. 

Caraccas.  — These  resemble  very  much  the  Guatemala  vari- 
eties. The  qualities  are  designated  by  analogous  names,  but 
they  are,  in  general,  less  esteemed  than  the  preceding. 

Mexican.  — They  hold  an  intermediary  rank  between  the  Ca- 
raccas and  Mexican. 

Brazil.  —  These  indigoes  are  in  small  rectangular  parallelo- 
piped  masses,  or  in  irregular  lumps  of  a  greenish  gray  color 
externally,  and  having  a  smooth  fracture,  a  firm  consistency,  and 
a  copper-colored  tint  of  greater  or  less  brilliancy. 

The  indigoes  of  Africa  and  Egypt.  — These  have  only  been 
manufactured  within  the  last  twenty  years ;  they  are  in  flat 
squares.  The  paste  is  fine  and  quite  light,  and  the  color  pure 
blue  or  bordering  on  violet.  The  varieties  are  distinguished  as 
fine  blue  and  good  violet  and  red. 


NOTES  UPON  INDIGO. 


19 


Indigoes  of  the  Isle  of  France  and  Senegal.  Rare  in  com- 
merce, but  of  good  quality. 

The  indigoes  of  the  inferior  qualities,  characterized  by  a  salt- 
like color,  bordering  more  or  less  upon  green  ;  by  a  coarse,  un- 
even, and  very  dense  paste ;  by  not  adhering  to  the  tongue,  and 
by  not  showing  a  coppery  color  when  scratched,  —  can  never  be 
employed  to  advantage,  notwithstanding  their  low  price.  The 
purchaser  of  these  qualities  must  be  guided  solely  by  the  results 
of  analysis ;  for  an  article  is  found  in  commerce  whose  rich- 
ness in  indigotine  does  not  exceed  twelve  to  fourteen  per  cent. 
The  presence  of  so  high  a  proportion  of  foreign  matter  prevents 
the  chemical  change  which  the  indigo  ou^ht  to  undergo  in  the 
dyeing  vat ;  and  this  foreign  matter,  added  to  the  deposits  of 
the  dyeing  vats,  causes  great  loss  of  the  coloring  matter.  These 
indigoes  should  be  used  as  little  as  possible,  especially  in 
the  cold  vats  used  for  dyeing  cotton  and  linen.  The  middle 
varieties  of  the  Bengal  and  Guatemala  indigoes,  and,  above  all, 
the  red  varieties,  produce  in  the  cold  vats  the  most  advantageous 
results.  The  lower  qualities  above  spoken  of  present  less  in- 
convenience in  the  hot  vats  used  for  dyeing  wool ;  and  it  is  for 
this  purpose  that  they  are  generally  used.  In  considering  the 
previous  observations,  the  wool  manufacturer  may  arrive  at  this 
conclusion  :  that  while  he  can,  with  less  loss  than  the  maker  of 
cotton  fabrics,  make  use  of  the  lowest  qualities  of  indigo,  he  will 
obtain  the  best  results  from  the  middle  qualities  of  the  reddish 
Bengal  indigoes. 

The  skilled  dealers  in  indigo  recognize  not  only  the  above 
distinctions,  founded  upon  the  country  of  production,  color,  and 
physical  qualities,  but  they  observe  whether  the  article  has  any  of 
the  following  defects,  which  are  designated  by  certain  well-under- 
stood terms  :  such  as  whether  the  indigo  is  sandy,  —  when  bril- 
liant points  are  observed  in  the  interior,  which  are  in  reality 
particles  of  sand ;  spotted,  that  is  to  say,  of  unequal  tint,  and 
marked  by  small  blackish  points  ;  ribboned,  marked  by  trans- 
versal bands  of  a  paler,  and  sometimes  red  color ;  burnt,  the 
pieces  having  a  scorched  appearance,  due  to  rapid  drying,  and 


20 


NOTES  UPON  INDIGO. 


separating  into  small  black  fragments  under  the  pressure  of  the 
hand ;  crumbly,  when  in  pieces  of  irregular  figure,  proceeding 
from  fractures  of  the  squares ;  cold,  when  the  indigo  does  not 
adhere  to  the  tongue.  The  above  classification  is  presented  with 
a  full  knowledge  that  these  distinctions  are  by  no  means  recog- 
nized in  the  ordinary  commerce  in  this  article.  It  is  not,  how- 
ever, without  interest  as  an  illustration  of  the  minute  attention 
given  to  this  subject  in  Europe,  where  a  higher  manufacture  re- 
quires a  nicer  investigation  of  the  qualities  of  materials  em- 
ployed. 

DETERMINATION  OF  THE  RICHNESS  AND  PURITY  OF  INDIGOES. 

It  is  evident  that  the  commercial  form  and  the  high  price  of 
this  drug  favor  fraud,  and  the  desire  to  illicitly  introduce  foreign 
substances  into  the  paste.  It  is  important,  therefore,  that  the 
purchaser  should  carefully  ascertain  the  actual  value  of  the  arti- 
cle wThich  he  is  to  use.  He  should  know  not  only  the  propor- 
tion of  indigotine  contained,  which  varies  in  the  commercial 
indigoes  from  twelve  to  seventy-five  per  cent,  but  the  hardness 
and  density.  A  good  indigo  ought  to  have  qualities  wrhich  can  be 
recognized  by  the  eye  and  touch  alone.  The  first  and  the  only 
examination  ordinarily  made  by  purchasers  is  in  respect  to  the 
physical  qualities  of  the  article.  Different  pieces  are  selected, 
and  their  fresh  fracture  is  attentively  observed.  The  purchaser 
observes  whether  the  squares  are  like  each  other,  and  if  the 
parts  of  the  same  piece  present  the  same  tint.  He  determines 
the  porosity  by  the  simple  means  of  applying  his  tongue  to  the 
fresh  fracture.  The  more  rapid  the  adherence  of  the  tongue, 
the  more  porous  the  indigo.  By  scratching  the  piece  with  his 
finger-nail,  he  determines  the  extent  of  the  coppery  reflection,  — 
an  important  test. 

From  all  these  characters,  taken  together,  the  purchaser  can 
form  quite  a  correct  idea  of  the  value  of  indigoes  in  general ; 
and  the  greater  number  of  dyers,  both  in  Europe  and  this 
country,  are  satisfied  to  make  their  purchases  with  only  this  phys- 
ical examination.    The  most  experienced  dealers  in  this  country 


NOTES  UPON  INDIGO. 


21 


make  no  other  examination  than  the  physical  one.  An  eminent 
indigo  broker  in  Boston  has  permitted  me  to  copy  the  following 
memoranda  for  the  physical  examination  of  indigo  from  his  note- 
book. 

The  chief  signs  of  good  indigo  are  its  lightness,  feeling  dry  when 
touched,  and,  when  broken,  appearing  ®f  a  beautiful  violet  blue.  Good 
indigo  swims  in  water ;  if  thrown  upon  burning  coals  it  emits  a 
violet-colored  smoke,  and  leaves  but  little  ashes. 

In  selecting  indigo  the  large  regularly  formed  cakes  should  be 
preferred,  —  those  of  a  fine,  rich  blue  color,  extremely  free  from 
the  white  adhesive  mould,*  and  of  a  clean,  neat  shape.  When 
broken,  it  should  be  of  a  bright  purple  cast,  of  a  close  and  compact 
texture,  free  from  specks  or  sand,  and  when  rubbed  with  the  nail 
should  have  a  beautiful  shiny  coppery  appearance  ;  when  burnt  in  a 
candle  it  should  fly  like  dust ;  that  which  is  heavy  and  dull  colored 
should  be  rejected.  Indigo  is  estimated  and  classed  in  commercial 
language,  as  follows  :  fine  blue,  ordinary  blue,  fine  purple,  inferior 
purple,  and  violet,  strong  copper,  and  ordinary  copper.  It  is  pur- 
chased by  the  factory  maund  (74|  lbs.  The  Bazaar  maund  is  82^ 
lbs.),  packed  in  cases  containing  on  an  average  2|  cwt.,  dammered 
(pitched)  and  covered  with  gunny  bagging. 

Still,  in  making  large  purchases,  as  a  measure  of  wise  precau- 
tion the  chemical  test  should  be  added.  This  is  used  to  ascer- 
tain the  proportion  per  cent  of  indigotine  which  a  given  indigo 
has.  The  determination  of  the  quality  of  indigotine  contained 
is  not  alone  sufficient  to-  fix  the  value  of  an  indigo.  With  an 
equal  yield  of  indigotine,  the  indigoes  are  always  to  be  preferred 
which  have  a  light  and  soft  paste  ;  and  for  the  preparation  of  the 
indigo  vat  the  preference  should  be  always  given  to  the  violet 
red  rather  than  to  the  clear  blue  indigoes. 

The  chemical  works  which  treat  of  this  subject  give  elaborate 
details  of  a  great  number  of  processes  for  determining  by 
chemical  tests  the  amount  of  indigotine,  or  the  coloring  mate- 
rial in  indigoes.    To  give  these  numerous  processes  would  only 


*  Many  experienced  purchasers  in  this  country  pay  no  regard  to  this  mould,  as  it 
weighs  scarcely  any  thing. —  Ed. 


22 


NOTES  UPON  INDIGO. 


confuse  the  reader.  In  our  own  confusion  upon  this  subject  we 
submitted  the  descriptions  of  these  various  processes  to  one  of 
the  most  eminent  and  practical  of  American  chemists,  Dr. 
Charles  T.  Jackson,  an  official  State  Assayer  for  the  State  of 
Massachusetts,  who  has  had  much  experience  in  testing  indigo, 
with  a  request  that  he  would  describe  the  process  which  he 
approves  and  practises.  He  has  obliged  us  by  the  following 
communication  :  — 

Boston,  Nov.  21,  1872. 
No.  47  Court  Street,  Room  4. 

John  L.  Hates,  Esq. 

Dear  Sir,  —  In  reply  to  your  inquiry  as  to  the  simplest  method 
of  analyzing  indigo,  I  would  say  that  I  first  ascertain  the  amount 
per  cent  of  earthy  matters  and  metallic  oxides,  in  the  samples 
brought  to  me,  by  burning  a  weighed  quantity  in  a  counterpoised 
platinum  crucible,  until  all  organic  matters  are  removed  or  con- 
sumed, and  then  weighing  the  ashes  obtained.  The  ash  is  then  sub- 
jected to  analysis  in  the  usual  way,  and  lime,  alumina,  peroxide  of 
iron,  and  some  other  earthy  impurities  are  separated. 

Then,  to  determine  the  amount  of  coloring  matter,  or  indigotine,  I 
make  use  of  a  standard  sample  of  pure  reduced  indigo,  which  is  dis- 
solved in  the  most  concentrated  sulphuric  acid,  and  diluted  with 
water  after  solution.  Then  I  ascertain  how  much  bleaching  powder 
(chloride  of  lime)  is  required  to  dissolve  the  solution.  This  is  the 
quantity  required  for  absolutely  pure  indigo. 

Now,  the  indigo  of  commerce  does  not  contain  more  than  say  from 
forty  or  fifty  per  cent  of  pure  indigotine,  and  of  course  will  require  a 
smaller  quantity  of  bleaching  powder  to  decolor  it;  or  the  quantity 
of  bleaching  powder  to  decolor  a  given  weight  of  pure  indigo  may 
be  weighed  out,  and  the  sample  to  be  compared  having  been  dissolved 
in  strong  sulphuric  acid,  and  diluted  with  water,  is  to  be  poured  in 
and  stirred  or  shaken  well  until  the  point  of  decoloration  is  ascer- 
tained. In  this  case  it  is  best  to  weigh  out  at  least  twice  as  much 
of  the  sample  to  be  tested  as  was  used  of  pure  indigo,  and  to  measure 
the  solution  in  a  graduated  glass  vessel,  —  an  alkalimeter,  for  exam- 
ple,—  so  that  by  measure  we  may  know  exactly  how  much  of  the 
sample  we  add  to  the  solution  of  bleaching  powder.  Thus  the 
relative  coloring  values  of  the  samples  may  be  readily  ascertained. 

If  you  have  no  purified  indigo  on  hand,  you  can  make  a  good  com- 


NOTES  UPON  INDIGO. 


23 


parative  trial  of  your  samples  against  a  perfectly  good  sample  of 
Bengal  indigo,  which  may  be  kept  for  a  standard  of  comparison. 
Very  useful  practical  results  may  thus  be  obtained. 

It  is  well,  however,  to  keep  on  hand  a  standard  sample  of  pure 
indigo,  prepared  from  reduced  or  white  indigo,  as  directed  by  Berzelius 
(vol.  vi.  page  3,  French  ed.,  1832),  and  in  Muspratt's  Chemistry 
applied  to  the  Arts  (Dyeing,  Indigo). 

In  the  analysis  by  reduction  of  indigo,  the  process  is  simply  as 
follows  :  Reduce  the  indigo  to  fine  powder,  and  weigh  it ;  weigh  out 
an  equal  quantity  of  pure  quicklime  (made  from  pure  white  marble)* 
Measure  in  a  graduated  vessel  a  certain  volume  of  water.  Slack  the 
lime  with  a  portion  of  this  water.  The  rest  of  this  water  is  to  be  used 
in  rubbing  up  the  indigo  in  a  mortar.  Then  the  slacked  lime  is  to  be 
mixed  with  the  indigo,  rubbing  the  substances  well  together.  Intro- 
duce the  whole  into  a  large  flask  ;  1 J  to  2  litres  (about  3  to  4 \  pints) 
of  water  is  required  for  1  gramme  (or  about  15  grains  of  indigo). 
The  flask  and  contents  are  then  to  be  exposed  to  a  heat  of  from  176° 
to  190°  F.  for  some  hours.  This  is  best  effected  in  a  water  bath.  By 
this  digestion  the  lime  is  made  to  combine  with  the  indigo  brown,  and 
the  coloring  matter  is  set  at  liberty.  Dissolve  in  the  liquor  a  little 
protosulphate  of  iron,  exempt  from  copper,  and  reduced  to  a  fine  pow- 
der. The  flask  is  to  be  corked  and  well  shaken,  and  allowed  to  cool. 
When  the  sediment  is  settled,  decant  the  clear  solution  by  means  of 
a  syphon  into  a  graduated  glass.  The  coloring  matter  oxidizes  by 
exposure  to  the  air  ;  and  to  favor  this  oxidation  and  to  keep  the  lime 
in  solution,  add  muriatic  acid  to  the  liquor.  When  the  liquor  has 
become  clear,  filter  and  collect  the  precipitate  on  a  weighed  filter, 
which  wash  with  hot  water,  and  dry  at  a  temperature  of  212°  F. 
Thus  we  can  learn,  by  weighing  the  filter  again,  how  much  indigotine 
is  contained  in  the  sample. 

If  we  make  use  of  200  measures  of  water,  and  have  drawn  off  50 
measures  of  the  solution  to  oxidate,  and  this  50  measures  has  pro- 
duced 10  grains  of  indigo,  the  whole  sample  evidently  contained  40 
grains  of  indigo  blue. 

This  method  serves  both  for  an  assay  of  the  sample  and  the  pro- 
duction of  a  standard  sample  of  pure  indigotine.  The  operation  may 
be  carried  on  upon  a  larger  scale  for  the  manufacture  of  a  standard 
sample. 

Yours  truly, 

C.  T.  Jackson. 


24 


NOTES  UPON  INDIGO. 


Dr.  Jackson  adds  the  following  note  :  — 

In  the  processes  given  I  have  not  referred  to  the  qualitative  anal- 
ysis or  testing  for  all  the  kinds  of  adulterations,  but  have  given  only 
valuation  of  the  coloring  power  of  indigo. 

I  have  had  occasion  to  search  indigo  for  Prussian  blue,  an  occa- 
sional adulterant.  This  is  ascertained  by  caustic  potash,  which  be- 
comes in  part  an  oxide  if  Prussian  blue  is  present.  This  acidulates 
with  muriatic  acid,  and,  tested  with  sulphate  of  iron,  proves,  by  for- 
mation of  Prussian  blue,  the  presence  of  the  ferrocyanide  of  potash 
in  the  solution,  and  hence  Prussian  blue  in  the  indigo.  Lime  and 
clay  are  the  usual  adulterants,  and  oxide  of  iron  is  often  present 
accidentally  or  from  the  clay  adulterants.  Starch  and  flour  are  rarely 
used,  as  they  add  little  to  the  weight. 

C.  T.J. 

COMMERCE  IN  INDIGO. 

Before  proceeding  to  a  consideration  of  the  practical  appli- 
cations of  indigo  in  manufacturing,  we  must  pause  to  make  some 
general  observations  upon  the  commerce  in  indigo. 

The  first  European  impulse  given  to  this  commerce  was  made 
by  the  Spanish  and  Portuguese.  They  not  only  imported  indigo 
from  the  Indies,  but  established  its  fabrication  in  their  colonies. 
To  them  we  owe  its  production  in  Guatemala,  Caraccas,  and 
Brazil.  The  French  exported  from  the  Island  of  San  Domingo, 
only,  in  1774,  2,350,000  pounds  weight  of  this  commodity. 
British  influence  was  exerted  in  favor  of  the  development  of  this 
article  in  the  American  colonies,  and,  in  1773,  in  the  space  of 
twelve  months,  over  a  million  pounds  of  indigo  were  ex- 
ported from  South  Carolina.  The  production  in  India  wTas  at 
that  time  of  little  importance.  It  was  not  until  1783  that  the 
attention  of  the  English  was  directed  to  the  culture  of  indigo 
in  India  for  European  consumption,  that  produced  by  the  natives 
being  all  consumed  in  their  own  manufactures.  In  the  hands  of 
the  English  this  product  rapidly  rose  to  be  the  most  important  of 
India,  in  a  commercial  view,  except  that  of  rice.  The  small  cost 
of  a  factory,  and  the  comparatively  small  capital  required  for 


NOTES  UPON  INDIGO. 


25 


this  production,  caused  the  indigo  culture  to  be  preferred  to  sugar 
planting.  The  importation  and  sale  of  this  commodity  at  the 
East  India  House,  in  1792,  amounted  to  581,827  lbs.,  while 
the  importation  into  Great  Britain  from  other  parts  of  the  world 
amounted  to  1,285,927  lbs.  In  1806  the  importation  from  the 
East  Indies,  and  sales  at  the  East  India  House,  amounted  to 
4,811,700  lbs.,  and  produced  in  sterling  money  £1,685,275. 
In  the  year  1862-63,  the  export  from  India,  and  the  destination 
of  supplies,  were  as  follows:  — - 


Destination. 

Quantity. 

Value. 

United  Kingdom  .... 

8,537,133  lbs. 

$1,627,035 

134,064 

26,949 

Arabian  and  Persian  Gulfs  . 

343,037 

33,385 

France  

1,922,120 

371,396 

85,680 

15,504 

295,269 

51,730 

9,577 

815 

Total.    .    .    .   \    .  . 

11,326,880  lbs. 

$2,126,814 

The  value  of  exports  in  1866  was  £1,861,501.  In  the  same 
year  the  imports  of  indigo  from  the  whole  of  Central  America, 
including  Honduras,  was  672,480  lbs.  The  consumption  of 
indigo  in  Great  Britain  did  not  increase  during  the  ten  years  end- 
ing with  1867.  This  stationary  demand,  notwithstanding  the 
fall  in  the  price  of  the  drug  and  increase  of  population,  is  attrib- 
uted by  McCulloch  principally  to  the  decreasing  use  of  blue 
cloth.  It  is  more  probably  due  to  the  substitution  of  cheaper 
dyes.  The  average  home  consumption  in  Great  Britain  for  seven 
years  ending  in  1867,  was  1,675,072  lbs.  per  year. 

The  importation  into  this  country  for  the  twenty  years  last 
past  is  shown  by  the  following  table,  kindly  prepared  at  our  re- 
quest by  the  chief  of  the  Bureau  of  Statistics  :  — 

4 


26 


NOTES  UPON  INDIGO. 


Statement  of  Imports  of  Indigo  into  the  United  States  during  the  Fiscal 
Tears  ended  June  30,  1853-1872. 


L  Years 
lune  30. 

INDIGO. 

Fiscal 
ended  «i 

FREE  OF  DUTY. 

DUTIABLE. 

Pounds. 

Dollars. 

Pounds. 

Dollars. 

loOo 

"1    OOI7   O  A  T 

1,387,847 

r\  a  <~i  (~>n  i-r 

947,367 

lo04: 

±,9o5,7o9 

1,282,367 

loOD 

z,Uy7,oy7 

1,151,516 

1856 

1,732,290 

1,063,743 

100/ 

l,Doo,Uo  / 

i,uiu,ouy 

1858 

1,647,767 

945,083 

1859 

1,773,868 

1,441,429 

1860 

1,707,116 

1,413,790 

1861 

185,039 

160,138 

719,563 

505,766 

1862 

2,501,052 

3,281,441 

1863 

885,834 

1,008,187 

178,364 

219,169 

1864 

684,813 

623,406 

897,821 

671,899 

1865 

741,438 

601,283 

415,575 

324,207 

1866 

798,855 

609,160 

44,660 

41,268 

1867 

1,069,506 

816,974 

1868 

870,164 

775,751 

1869 

1,574,449 

1,649,550 

1870 

1,270,579 

1,203,664 

1871 

1,994,172 

2,052,222 

1872 

1,526,869 

1,484,744 

EDWARD  YOUNG,  Chief  of  Bureau. 

Bureau  of  Statistics,  Nov.  16,  1872. 


The  extraordinary  quantity  imported  in  1862,  we  hardly  need 
remark,  was  due  to  the  demand  for  consumption  in  army 
cloths.  Indigo  imported  directly,  was  made  free  of  duty  in 
1861.  The  duty  which  appears  by  the  above  table  to  have 
been  charged  since  that  period,  was  upon  indigo,  the  product  of 
India,  imported  by  way  of  England,  which  was  subject  t6  an 
extra  duty  of  ten  per  cent. 

The  indigo  consumed  in  the  United  States  is  generally  sup- 
plied by  the  Boston  and  New  York  Calcutta  houses,  who  have 
either  an  American  partner  resident  in  Calcutta,  or  who  employ 
a  resident  American  as  agent.  Indigo,  like  other  Calcutta  goods, 


NOTES  UPON  INDIGO. 


27 


is  sold  through  the  agency  of  brokers,  who  receive  on  this 
article  a  commission  of  one  per  cent.  The  value  of  the  article  is 
known  almost  daily  in  these  cities  by  telegrams,  giving  exact 
information  of  the  state  of  the  trade,  transmitted  from  Calcutta 
as  often  as  every  five  days.  Some  of  the  brokers  publish 
monthly  circulars,  showing  the  stock  of  indigo  with  other  Cal- 
cutta goods  on  hand  in  our  market.  The  regular  trade  reports 
issued  by  the  India  merchants  show  that  the  higher  qualities  of 
indiw  do  not  come  to  our  market.  The  following  is  an  extract 
from  a  report  of  Whitney,  Brother,  &Co.,  of  1871 :  — 


Indigo  for  Continent   fine  350  to  362  rupees. 

„       „  „    good  330  „  345  „ 

„  „    middling  310  „  325  „ 

American  consuming   fine  280  „  300  „ 

  good  250  „  275  „ 

  middling  200  „  240  „ 

„  „    low  and  ordinary  150  „  170  „ 


At  the  present  moment  there  is  great  depression  in  the  trade 
in  this  article.  The  last  telegrams  show  a  decline  of  price  in 
the  Indian  trade  in  this  article  of  from  fifty  to  seventy-five  per  cent 
from  the  prices  of  last  year  ;  and  the  apprehension  is  even  enter- 
tained that  indigo  is  going  out  of  use,  the  dreaded  competitors 
being  the  aniline  dyes,  and  particularly  the  Nicholson  blue. 
We  maybe  presumptuous  in  giving  our  opinion  on  the  question, 
but  we  hazard  the  prediction  that,  notwithstanding  the  temporary 
popularity  of  the  cheap  substitutes,  a  reaction  will  take  place  in 
favor  of  that  "  wonderful  and  most  valuable  production,"  whose 
importance  as  a  dye  has  been  held  in  India  for  thousands  of 
years  and  Europe  for  two  centuries,  "greatly  to  exceed  any 
other."  * 

*  The  "  Dictionnaire  Universel  du  Commerce,"  &c,  published  in  1861,  contains  an 
exhaustive  article  on  the  commerce  in  indigo,  by  M.  S.  Beekrode.  From  the  state- 
ments of  this  writer,  it  appears  that  the  consumption  of  indigo  was  estimated,  in  1835, 


as  follows  :  — 

Great  Britain   1,214,380  kilograms  (2,683,779)  lbs. 

France   912,915  (2,017,542)  „ 

United  States   130,000        „  (277,300)  „ 

Other  countries   2,435;473        „         (5,382,395)  „ 


Total   4,692,768  kilograms  (10,362,016)  lbs. 


28 


NOTES  UPON  INDIGO. 


FORMER  PRODUCTION  IN  THE  CAROLINAS. 

As  pertinent  to  the  commercial  branch  of  our  subject,  we  must 
briefly  notice  the  remarkable  facts  of  the  sudden  growth  and 
equally  sudden  and  extraordinary  extinction  of  the  production  of 
indigo  in  the  Carolinas.  Indigo  was  for  many  years  the  second 
great  staple  of  South  Carolina.  So  highly  was  this  staple  esti- 
mated that  the  historian  of  the  State  declares  that  "  it  proved 
more  really  beneficial  to  Carolina  than  the  mines  of  Mexico  or 
Peru  are  or  ever  have  been  to  Old  or  New  Spain."  Its  intro- 
duction was  the  happy  result  of  a  woman's  culture  and  energy. 
In  the  early  part  of  the  last  century,  the  indigo  plant  had  been 
extensively  cultivated  in  the  West  India  Islands,  which  then 
furnished  the  chief  supply  of  Europe.  The  governor  of  Antigua, 
George  Lucas,  whose  home  plantation  was  at  Wappoo  in  Caro- 
lina, having  observed  the  fondness  of  his  daughter,  Miss  Eliza 
Lucas,  afterwards  the  mother  of  General  Charles  Cotes  worth 
Pinckney,  for  the  culture  of  plants,  was  in  the  habit  of  sending 
to  her  tropical  seeds  to  be  sowed  on  his  plantation  at  Wappoo. 
Among  others,  he  sent  her  some  seeds  of  the  indigo  plant  culti- 
vated in  the  West  Indies.   She  planted  them  for  two  years  ;  but 


The  approximate  consumption  in  1859  is  stated  as  follows  :  — 


Great  Britain  •  .    .  800,000  kilograms  (1,768,000)  lbs. 

France   800,000  „  (1,768,000)  ,, 

United  States   400,000  ,,  (    884,000)  „ 

Russia   860,000  „  (1,900,600)  „ 

The  Zollverein   1,250,000  „  (2,762,500)  „ 

Switzerland   150,000  ,,  (  331,500)  „ 

Austria   400,000  •  „  (   884,000)  „ 

Other  countries   300,000  „  (  '663,000)  „ 


Total   4,960,000  kilograms  (10,961,600)  lbs. 

The  average  production  in  1859  is  estimated  as  follows  :  — 

Bengal,  Madras,  &c   3,500,000  kilograms  (7,735,000^  lbs. 

Java   550,000        „        (1,215,500)  „ 

Central  America   300,000        „        (   663,000)  „ 

Other  sources   100,000        „        (  221,000)  „ 


Total   4,450,000  kilograms  (9,834,500)  lbs. 


As  the  maximum  annual  consumption  in  1859  is  setdown  at  5,000,000  kilograms,  the 
author  concludes  that  the  average  production  at  that  time  did  not  surpass  the  require- 
ments of  the  dyers  of  the  whole  world. 


NOTES  UPON  INDIGO. 


29 


the  seeds  failed  to  germinate,  or  were  killed  by  the  frost.  On  the 
third  year's  trial,  in  1741  or  1742,  she  was  successful.  Governor 
Lucas,  on  hearing  that  the  plants  had  ripened  and  produced 
seed,  sent  from  Montserrat  a  person  skilled  in  making  indigo. 
Vats  were  built  on  Wappoo  Creek,  and  there  the  first  American 
indigo  was  manufactured.  The  attempts  of  the  expert  to  con- 
ceal his  processes  were  defeated  by  the  vigilance  of  Miss  Lucas. 
The  process  of  manufacture  was  made  known.  Seeds  from  the 
AYappoo  plantation  were  freely  distributed  and  successfully 
planted  ;  and  the  culture  of  indigo  became  common.  In  1747, 
a  considerable  quantity  of  indigo  was  sent  to  England,  which 
induced  the  merchants  trading  with  Carolina  to  petition  parlia- 
ment for  a  bounty  on  Carolina  indigo.  In  1748,  an  act  of 
parliament  was  passed  granting  a  bounty  of  sixpence  per  pound 
on  indigo  raised  on  British-American  plantations  and  imported 
directly  to  Britain  from  its  place  of  growth.  This' act  stimulated 
the  planters  of  Carolina  to  double  vigor  in  the  production  of 
this  new  material  for  export.  "  Many  of  them,"  says  Dr.  Ram- 
say, "doubled  their  capital  every  three  or  four  years  by  planting 
indigo."  In  the  year  1754,  the  export  of  indigo  from  the 
province  amounted  to  216,924  lbs.,  and  in  the  years  1772  and 
1773  the  export  had  risen  to  1,107,661  lbs.  The  production  was 
greatly  checked  by  the  war  of  the  Revolution.  Near  the  close  of 
the  century  the  large  importations  from  India  lowered  the  price, 
so  as  to  make  the  planting  unprofitable.  In  the  mean  time, 
the  culture  of  cotton  had  sprung  up  under  the  protective  tariff  of 
1789.  The  grounds  suitable  for  indigo  planting  were  equally 
fitted  for  cotton,  and  were  for  the  most  planted  with  the  new 
staple.  It  is  curious  to  observe  how  the  former  was  displaced 
by  the  latter  staple.  The  export  of  indigo  from  Charleston  in 
1797  was  96,121  lbs.  :  in  1800,  it  fell  to  3,400  lbs.  During 
the  same  years,  the  exports  of  cotton  rose  from  one  million  to 
six  and  a  half  million  pounds.  The  production  of  American 
indigo  appears  to  have  revived  from  time  to  time  up  to  1829. 
A  writer  of  that  period  in  Silliman's  Journal  of  Science  esti- 
mates—  although  it  would  seem  on  doubtful  authority  —  the  pro- 
duction of  indigo  in  the  United  States  at  20,000  lbs.    The  price 


30 


NOTES  UPON  INDIGO. 


of  the  American  article  had  fallen,  owing  to  the  great  quantity 
of  extractive  which  it  contained,  to  fifty  cents  per  pound,  while 
the  Bengal  indigo  was  worth  $1.15  per  pound.  We  have  no 
data  as  to  its  production  at  the  present  time,  but  infer,  from  the 
fact  that  no  reference  has  been  made  to  this  product  in  the 
Government  Agricultural  Reports  for  many  years  past,  that 
the  production,  if  any,  is  too  unimportant  to  be  noticed. 

INDUSTRIAL  APPLICATION  OF  INDIGO. 

All  the  applications  of  indigo  require  that  the  material  should 
first  be  reduced  to  an  impalpable  powder.  It  is  better  to  grind 
it  with  water,  to  prevent  the  loss  of  material  in  the  form  of 
powder,  although  the  dry  pulverization  is  necessary  when  the 
indigo  is  to  be  used  for  the  manufacture  of  the  sulphate.  To 
facilitate  the  grinding  the  material  into  a  paste,  it  should  be  pre- 
viously soaked  in  hot  water  from  one  to  three  hours.  The 
grinding  on  a  small  scale  may  be  done  by  a  very  simple  appa- 
ratus. This  is  a  hemispherical  vessel  of  copper  or  cast-iron, 
eighteen  inches  in  diameter,  furnished  at  the  edge  with  two  han- 
dies.  The  workman,  sitting  astride  a  bench,  places  the  vessel 
before  him,  in  which  he  places  three  heavy  cast-iron  balls,  the  in- 
digo which  has  been  softened,  and  a  sufficient  quantity  of  water. 
Holding  the  basin  by  the  handles,  he  gives  it  a  circular  oscillatory 
movement,  in  such  a  manner  that  the  balls,  following  this  mover 
ment,  crush  the  indigo  which  surrounds  them  ;  after  which  the 
contents  are  poured  into  another  vessel,  water  is  added,  and  the 
material  is  stirred.  The  portions  incompletely  ground  are  made 
to  reunite  themselves  at  the  bottom  by  means  of  regular  blows 
with  a  hammer  on  the  rim  of  the  vessel.  The  upper  liquid  is 
decanted,  and  the  deposit  is  submitted  to  a  new  manipulation  in 
the  basin. 

In  large  establishments  the  grinding  is  done  by  machinery. 
An  apparatus  highly  recommended,  consists  of  two  circular 
plates  of  cast-iron,  arranged  horizontally  and  slightly  separated, 
one  from  the  other,  which  are  rapidly  rotated  by  power,  in 
inverse,  directions.  The  interior  surfaces  of  these  disks  are  pro- 
vided with  deep  grooves  radiating  in  a  curved  line  from  the 


NOTES  UPON  INDIGO. 


31 


centre  to  the  circumference,  and  diminishing  in  depth  in  the 
same  direction.  The  indigo  which  has  been  previously  softened 
enters  between  the  two  plates  by  an  opening  in  the  centre  of  the 
upper  one,  and  escapes  in  a  thin  paste  by  the  circumference. 

The  application  of  indigo  to  the  coloring  of  textile  fabrics  re- 
quires the  complete  dissolving  of  the  substance,  for  which  the 
mechanical  division  is  only  a  preliminary.  There  are  only  two 
known  means  of  dissolving  this  substance:  1.  By  reduction; 
2.  By  the  action  of  concentrated  sulphuric  acid.  The  first 
means  allows  indigotine  to  be  regenerated  ;  and,  when  the  dyeing 
is  completed,  it  is  pure  indigotine  which  adheres  to  the  colored 
fibre.  By  the  second  means,  or  dissolving  by  sulphuric  acid, 
the  coloring  material  enters  into  a  new  combination,  from  which 
it  can  never  be  separated  :  it  becomes  a  new  substance,  endowed 
with  new  and  special  properties. 

The  fixing  of  Indigotine  by  means  of  Reduction.  — In  this 
method  the  operator  avails  himself  of  one  qf  the  most  remark- 
able qualities  of  indigotine  :  this  is  the  facility  with  wrhich  this 
body  takes  up  hydrogen,  and  becomes  transformed  into  a  color- 
less substance,  wrhich  is  soluble  in  favor  of  alkaline  or  alkaline- 
earthy  bases,  and  is  susceptible  of  reproducing  indigotine  by 
simple  oxidation  in  contact  with  air.  This  hydrogenized  sub- 
stance is  called  white  indigo.  Blue  indigo,  or  indigotine,  is 
insoluble  except  by  concentrated  sulphuric  acid ;  and  this 
insolubility  gives  it  its  superiority  to  all  other  blue  dyes.  Not 
being  soluble,  it  cannot,  as  blue  indigo,  attach  itself  to  the 
material  to  be  dyed  ;  but  in  the  soluble  form  of  white  indigo 
it  can  perfectly  penetrate  the  fibre.  If  by  any  means  of  oxi- 
dation we  can  transform  the  white  indigo  into  bl*ie  indigotine, 
the  latter  becomes  insoluble,  and  is  imprisoned  in  the  pores  of 
the  fibre.  This  is,  briefly,  the  whole  theory  of  the  use  of  indigo 
in  dyeing  or  printing,  although  the  reaction  may  be  applied  in 
different  ways  to  the  coloring  of  fibres,  such  as  — 

1.  The  indigo  is  dissolved  by  means  of  an  alkaline  reduction 
in  a  vat,  and  the  fibre  is  immersed  in  the  bath.  This  is  the 
common  blue  vat. 

2.  The  solution  prepared  beforehand  is  painted  by  a  hair 


32 


NOTES  UPON  INDIGO. 


pencil  and  printed  by  a  stamp  or  roller  upon  only  certain  parts 
of  the  tissues.    This  is  the  pencil-blue. 

3.  The  white  indigo  is  precipitated  under  the  form  of  a  paste,  in 
combination  with  a  metallic  oxide  having  strong  reducing  power, 
such  as  hydrated  protoxide  of  tin,  which  prevents  the  too  rapid 
reoxidation  of  the  indigotine.  The  thickened  paste  is  printed, 
and  the  tissue  is  placed  in  an  alkaline  bath  (lime  or  soda), 
which,  displacing  the  oxide  of  tin,  forms  a  soluble  combination 
of  white  indigo.  The  latter  can  then  penetrate  the  fibre,  and 
afterwards  become  fixed  by  reoxidation.  This  is  the  printer's 
solid  blue. 

4.  The  finely  ground,  but  not  dissolved  indigo,  is  placed  upon 
the  tissue  in  such  conditions  that  it  can  be  dissolved  and  reduced 
in  place.  This  done,  the  fixing  of  the  indigotine  is  effected  by 
oxidation.    This  is  the  method  for  China  blue  or  bleu  faience. 

Without  dwelling  upon  the  details  of  these  methods,  we 
hasten  to  a  consideration  of  the  most  important  of  all  the  appli- 
cations of  indigo  :  — 

v  DYEING  BY  THE  INDIGO  VAT. 

The  Copperas  Vat.  —  For  dyeing  cotton,  the  method  of  reduc- 
tion found  by  experience  to  be  the  most  convenient  and  practi- 
cal is  founded  upon  the  action  of  the  hydrate  of  the  protoxide  of 
iron  in  the  presence  of  lime.  The  hydrated  protoxide  of  iron 
is  obtained  from  sulphate  of  iron  (green  vitriol,  or  copperas) 
with  freshly  burned  lime.  Certain  precautions  should  be  ob- 
served in  the  use  of  these  materials.  The  copperas  used  for  the 
preparation  of  these  vats  should  be  free  from  sulphate  of  cop- 
per, because  jhe  oxide  of  copper  which  would  be  formed  in  the 
vats  rapidly  oxidizes  the  reduced  indigo,  and  causes  its  precipita- 
tion in  the  bath.  The  copperas  ought  not  to  contain  red  oxide  of 
iron,  nor  sulphate  of  alumina.'  The  coppery  or  oxidized  vitriol 
may  be  purified  by  boiling  the  solution  with  pieces  of  iron,  which 
precipitates  the  iron  and  neutralizes  the  oxide.  The  lime  ought 
to  be  pure,  containing  no  magnesia  ;  when  slacked  lime  has  been 
exposed  to  the  air,  even  for  a  short  time,  it  absorbs  carbonic 
acid,  and  becomes  converted  into  chalk.    The  lime,  therefore, 


NOTES  UPON  INDIGO. 


33 


should  always  be  newly  slacked.  The  ingredients,  then,  of  a 
copperas  vat  are  water,  pure  or  purified  green  vitriol,  indigo 
ground  into  a  homogeneous  impalpable  paste,  and  pure  and 
freshly  slacked  lime.  The  proportions  used  in  different  estab- 
lishments are  exceedingly  variable.  Those  which  answer  for  a 
laboratory  vat,  or  a  small  vat  used  for  precipitating  the  white 
indigo  immediately  for  printing,  are:  indigo,  one  part;  sul- 
phate of  iron,  two  parts ;  slacked  lime,  three  parts.  These  pro- 
portions are  not  enough  for  the  large  vats  used  in  dyeing  pieces. 
In  them  it  is  necessary  to  make  the  quantities  of  lime  and  sul- 
phate of  iron  larger  than  the  theory  of  the  vat  requires.  The 
excess  of  lime  and  hydrate  of  iron  serve  the  purpose,  whenever 
the  vat  is  stirred,  to  repair  the  losses  of  indigo  caused  by  its 
oxidation  from  contact  with  the  air.  Schutzenberger  gives  the 
proportions  generally  used  by  the  dyers  of  France,  as  follows  :  — 

Indigo  1  part. 

Crystallized  sulphate  of  iron  3  „ 

Freshly  slacked  lime  3  „ 

Others,  he  says,  use  more  lime  than  copperas,  as  in  the  follow- 
ing proportion  :  — 

Indigo  2  parts. 

Sulphate  of  iron  5.5  „ 

Quicklime  6.5  „ 

M.  de  Kseppelin,  who  is  especially  familiar  with  the  cotton 
dyeing  in  Mulhouse,  describes  the  ordinary  vats  for  cotton  dyeing 
as  bound  with  iron,  and  placed  on  the  level  of  the  ground.  They 
hold  from  3,000  to  4,000  litres  (1,055  gallons)  of  liquid.  In 
preparing  them  the  dyer  fills  them  about  three-quarters  full  of 
water,  and  pours  in  a  milk  of  lime,  prepared  with  45  kilograms 
(100  lbs.)  of  freshly  slacked  lime  ;  a  fine  liquid  paste  having  been 
previously  made  from  15  kilograms  (33  lbs.)  ground  in  water. 
This  is  added  to  the  lime  in  the  vat  by  portions,  the  liquid  in  the 
vat  being  stirred  up  by  a  rake  after  each  portion  of  the  indigo  paste 
has  been  added.  The  indigo  becomes  dissolved  in  about  twenty- 
four  hours,  when  the  vat  can  be  used.  After  describing  the  manner 
in  which  the  frame,  or  champignon,  containing  the  goods  to  be 


34 


NOTES  UPON  INDIGO. 


dyed  is  arranged  and  immersed  in  the  vat,  this  author  continues  : 
w  It  will  be  understood  that  the  vat  is  composed  according  to  the 
degree  of  intensity  of  the  color  which  is  sought  to  be  obtained, 
and  that  hues  more  or  less  deep  may  be  obtained  by  means  of 
more  or  fewer  repeated  immersions  of  the  fabric  to  be  dyed. 
After  each  immersion  the  champignon  is  lifted  out  of  the  vat, 
and  the  fabrics  are  left  to  ungreen  themselves  by  contact  with 
the  air.  (It  must  be  observed  that,  although  soluble  indigo  is 
called  white,  because  it  is  without  color  when  carefully  prepared 
in  the  laboratory,  the  goods,  when  first  taken  from  the  ordinary 
vat,  are  of  a  green  color.)  Exposed  to  the  air,  the  soluble 
indigo  is  precipitated  in  the  state  of  blue  indigo  upon  the  fibres 
of  the  tissue.  This  oxidation,  or  dehydryzation,  may  be 
hastened  by  plunging  the  tissue  into  a  vat  containing  a  solution, 
very  much  diluted  with  water,  chloride  of  lime,  bichromate  of 
potash,  or  sulphuric  acid.  The  first  two  act  as  oxidizing  agents  ; 
the  last  facilitates  the  restoring  of  the  blue  indigo  by  depriving 
it  of  the  lime  which  is  in  excess  in  the  solution  of  indigo  which 
the  tissue  has  imbibed  from  the  vat." 

He  adds  further  :  "  To  facilitate  the  formation  of  blue  indigo 
in  the  interior  of  the  fabrics,  the  stuff  to  be  dyed  may  be  pre-' 
viously  impregnated  by  a  saline  solution,  which  has  the  property 
of  precipitating  the  white  indigo  from  the  alkaline  solution,  and 
of  fixing  itself  more  rapidly  upon  the  tissue.  Oxide  of  copper 
and  oxide  of  manganese  possess  these  properties  in  a  high  de- 
gree, and  are  used  in  many  establishments  to  hasten  the  dyeing 
process,  and  produce  an  economy  in  raw  materials.  The  pieces 
of  cloth  are  placed  in  a  solution  of  sulphate  of  copper,  in  the 
proportion  of  15  to  20  grams  to  the  litre  (2.11  pints),  and 
lightly  thickened  with  starch.  The  fabrics,  thus  impregnated 
by  a  kind  of  mordant,  before  receiving  the  blue  dye  are  first 
passed  through  a  weak  bath  of  milk  of  lime,  which  fixes  the 
oxide  of  copper  upon  the  tissue.  The  blues  thus  obtained  are 
more  intense,  and  have  a  peculiar  lustre.  This  process  is  used 
in  Austria  and  Germany,  where  cotton  fabrics  are  printed  on 
both  sides  of  the  tissue." 

Coming  to  the  English  authorities,  Dr.  Grace  Calvert,  in 


NOTES  UPON  INDIGO. 


35 


his  recent  lectures  before  the  Society  of  Arts,  speaking  of  the 
cold  vat  for  dyeing  cotton,  says:  "The  oldest,  and  still  most 
generally  employed  method  of  preparing  cold  vats,  consists  of 
putting  into  a  vat  containing  about  2000  gallons  of  water  CO 
lbs.  of  indigo,  very  finely  powdered,  180  lbs.  of  slacked  lime,  and 
120  lbs.  of  sulphate  of  protoxide  of  iron,  or  green  vitriol  (free 
from  any  trace  of  copper  salt),  the  two  latter  substances  being 
added  from  time  to  time.  The  greater  part  of  the  lime  used 
unites  with  the  sulphuric  acid  of  the  iron  salt,  to  produce  sul- 
phate of  lime  or  gypsum  ;  and  the  liberated  protoxide  of  iron 
removes  the  oxygen  from  the  indigo,  becoming  converted  into 
saline  oxide,  whilst  the  reduced  indigo  dissolves  in  the  excess 
of  lime  employed." 

He  adds  the  following  facts,  which  may  be  of  practical 
value  :  — 

Messrs.  R.  Schloesser  &  Co.,  of  Manchester,  have  intro- 
duced within  the  last  year  or  two  a  marked  improvement,  in  the 
preparation  of  cold  vats,  which  removes  the  great  objections  of 
the  bulky  precipitate  of  sulphate  of  lime,  the  formation  of  an 
oxide  of  iron,  and  the  loss  of  indigo  by  its  combination  with  the 
oxide  of  iron.  The  bath  remaining  much  more  fluid,  the  pieces 
are  less  apt  to  be  spotted,  and  a  better  class  of  work  is  pro- 
duced. To  carry  out  their  process,  they  add  to  the  ordinary 
2,000  gallon  vat  20  lbs.  of  ground  indigo,  30  lbs.  of  iron  bor- 
ings, 30  lbs.  of  their  remarkable  powdered  zinc,  and  35  lbs.  of 
quicklime ;  the  whole  is  stirred  up  from  time  to  time,  for 
twenty-four  hours,  when  it  is  ready  for  use.  If  the  bath  is  not 
considered  sufficiently  strong,  a  little  more  lime  and  zinc  are 
introduced.  The  chemical  theory  of  the  process  is,  that  the 
zinc,  under  the  influence  of  the  lime,  decomposes  the  water,  com- 
bining with  its  oxygen,  and  the  hydrogen  thus  liberated  removes 
oxv^en  from  the  indigo  which  then  dissolves  in  the  lime." 

An  excellent  description  of  the  processes  employed  at  Man- 
chester, England,  in  preparing  and  working  the  copperas,  or 
cold  vat,  is  given  in  Urie's  "  Dictionary  of  Manufactures." 
64  The  ingredients  necessary  for  setting  the  vat  are  copperas, 
newly  slacked  quicklime,  and  water.    Various  proportions  of 


36 


NOTES  UPON  INDIGO. 


these  ingredients  are  employed,  as,  for  instance:  1  part  by 
weight  of  indigo  (dry),  3  parts  of  copperas,  and  4  of  lime ;  or, 
1  of  indigo,  of  copperas,  and  3  of  lime  ;  or,  8  of  indigo, 
14  of  copperas,  and  20  of  lime ;  or,  1  of  indigo,  -|  of  copperas, 
and  20  of  lime ;  or  1  of  indigo,  |  of  copperas,  and  1 
of  lime.  The  sulphate  of  iron  should  be  as  free  as  possi- 
ble, from  red  oxide  of  iron,  as  well  as  sulphate  of  copper,  which 
reoxidize  the  reduced  indigo-blue.  The  vat,  having  been  filled 
with  wrater  to  near  the  top,  the  materials  are  introduced,  and  the 
whole,  after  being  well  stirred  several  times,  is  left  to  stand  for 
about  twelve  hours.  The  chemical  action  which  takes  place  is 
very  simple.  The  protoxide  of  iron,  which  is  set  at  liberty  by 
the  lime,  reduces  the  indigo-blue ;  and  the  indigo,  which  is  then 
dissolved  by  the  excess  of  lime,  forming  a  solution,  which,  on 
being  examined  in  a  glass,  appears  perfectly  transparent  and 
of  a  pure  yellow  color,  and  becomes  covered,  whenever  it  comes 
in  contact  with  the  air,  with  a  copper-colored  pellicle  of  regen- 
erated indigo-blue.  The  sediment  at  the  bottom  of  the  vat 
consists  of  sulphate  of  lime,  peroxide  of  iron,  and  the  insoluble 
impurities  of  the  indigo,  such  as  indigo-brown  in  combination 
with  lime,  as  well  as  sand,  clay,  &c.  If  an  excess  of  lime  is 
present,  a  little  reduced  indigo-blue  will  also  be  found  in  the 
sediment  in  combination  with  lime.  .  .  .  The  dyeing  process  itself 
is  very  simple.  The  vat  having  been  allowTed  to  settle,  the 
goods  are  plunged  into  the  clear  liquor,  and,  after  being  moved 
about  in  it  for  some  time,  are  taken  out,  allowed  to  drain,  and 
exposed  to  the  action  of  the  atmosphere.  While  in  the  liquid, 
the  fabric  attracts  a  portion  of  the  reduced  indigo-blue.  On 
now  removing  it  from  the  liquid,  it  appears  green,  but  soon 
becomes  blue  on  exposure  to  the  air,  in  consequence  of  the  oxi- 
dation of  the  reduced  indigo-blue.  On  again  plunging  it  into 
the  vat,  the  deoxidizing  action  of  the  vat  does  not  again  remove 
the  indigo-blue  which  has  been  deposited  within  and  around  the 
vegetable  or  animal  fibre,  but,  on  the  contrary,  a  fresh  portion 
of  the  reduced  indigo-blue  is  attracted,  which,  on  removal  from 
the  liquid,  is  again  oxidized  like  the  first,  and  the  color  thus 
becomes  a  shade  darker.    By  repeating  this  process  several 


NOTES  UPON  INDIGO. 


37 


times  the  requisite  depth  of  color  is  attained.  This  effect  can- 
not, in  any  case,  be  produced  by  one  immersion  in  the  vat, 
however  strong  it  may  be.  The  beauty  of  the  color  is  increased 
by  finally  passing  the  goods  through  diluted  sulphuric  or  muri- 
atic acid,  which  removes  the  adhering  lime  and  oxide  of  iron. 
After  being  used  for  some  time,  the  vat  should  be  refreshed  or 
fed  with  copperas  and  lime,  upon  which  occasion  the  sediment 
must  first  be  stirred  up,  and  then  allowed  to  settle  again,  so  as 
to  leave  the  liquor  clear.  The  indigo-blue,  however,  is  in  course 
of  time  gradually  removed,  and  by  degrees  the  vat  becomes 
capable  of  dyeing  only  pale  shades  of  blue.  When  the  color  pro- 
duced by  it  is  only  very  faint,  it  is  no  longer  worth  while  using 
it,  and  the  contents  are  then  thrown  away.  In  dyeing  cotton 
with  indigo,  it  seems  to  be  essential  that  the  reduced  indigo-blue 
should  be  in  contact  with  lime.  If  potash  or  soda  are  used  in 
its  place,  it  is  impossible  to  obtain  dark  shades  of  blue." 

FERMENTING  VATS  FOR  WOOL  DYEING. 

The  application  of  indigo-blue  to  wool  and  woollen  tissues  is 
always  made  by  means  of  vats,  which  have  special  names  ;  as, 
the  pastel  or  woad  vat,  the  urine  vat,  German  vat,  molasses  vat, 
&c.  The  reduction  or  hydrogenation  of  the  indigo-blue  is  the 
result  of  a  peculiar  fermentation,  which  is  developed  within  an 
alkaline  liquor  by  means  of  nitrogenized  substances  and  bodies 
rich  in  sugar  or  hydrocarbonized  substances.  It  is  known  that 
in  these  conditions,  especially  where  the  temperature  is  slightly 
raised,  the  sugar  is  converted  into  butyric  acid,  and  at  the  same 
time  carbonic  acid  and  hydrogen  are  set  free.  We  find  here 
the  source  of  the  nascent  hydrogen  wThich  fixes  itself  upon  the 
indigo-blue,  and  transforms  it  into  white  indigo,  which  is  soluble 
in  the  alkalies  of  the  vat.  It  has  recently  been  observed  that 
the  butyric  fermentation  proceeds  from  the  development  of  mi- 
nute infusoria.  These  animalcule  live  without  any  supply  of 
oxygen,  and,  in  fact,  are  killed  in  its  presence.  They  therefore 
live  at  their  ease  in  the  vat  of  reduced  indigo,  where  no  oxygen 
is  permitted  to  enter. 

The  ingredients  most  usually  employed  for  furnishing  the 


38 


NOTES  UPON  INDIGO. 


hydrocarbonaceous  substances  for  fermentation  are  bran  and 
ground  madder,  although  molasses  is  sometimes  used.  The 
nitrogenized  material  is  found  in  the  woad  or  pastel,  which  is 
often  added  in  very  large  proportions  to  the  fermenting  vats.  It 
is  observed  by  the  chemists  who  have  studied  this  subject  most 
carefully,  that  the  preparation  of  vats,  founded  upon  the  princi- 
ple of  fermentation,  does  not  repose  upon  principles  so  sure 
and  constant  as  those  of  the  copperas  vat,  and  that  many  unfore- 
seen accidents  interpose  to  disturb  the  work  of  an  inexperienced 
dyer.  The  phenomena  in  fermentations  are  often  complex.  It 
is  admitted  that  in  these  phenomena  theory  has  not  said  its 
last  word,  and  that  empiricism  is  often  more  fortunate  than 
science.  In  conducting  the  operations  of  the  warm  fermenting 
vat,  the  conceit  of  the  practical  dyer,  so  often  remarked  upon, 
is  not  without  foundation.  By  practical  experience  and  the  tra- 
ditions of  his  art  he  has  acquired  a  knowledge'  of  the  almost 
insensible  modification  in  conditions  which  can  change  or  arrest 
the  chemical  reaction.  It  is  the  knowledge  of  the  workman,  a 
knowledge  almost  instinctive,  which  can  never  be  communi- 
cated to  the  books,  and  which  is  most  respected  by  those  most 
profoundly  informed  in  theory. 

The  Woad  or  Pastel  Vat.  — In  former  times  woad,  already 
referred  to,  was  the  only  material  known  to  the  dyers  of  Europe 
for  producing  the  blue  color  of  indigo.  For  dyeing  wool, 
the  use  of  woad,  now  abandoned  wholly  in  cotton  dyeing,  has 
been  retained  to  the  present  day,  generally  for  the  purpose 
of  exciting  fermentation,  and  without  regard  to  its  effect  in 
imparting  color  to  the  material  to  be  dyed ;  for  the  woad 
grown  in  England,  and  used  in  the  dye-houses  of  that  country, 
contains  no  trace  of  coloring  matter.  The  woad,  or  pastel,  grown 
in  the  warmer  districts  of  France  contains  about  two  per  cent 
of  indigotine,  which  is  regarded  in  that  country  as  an  important 
addition  to  the  coloring  material,  especially  for  improving  the 
tone  of  the  color.  Various  substitutes,  such  as  rhubarb  leaves, 
turnip  and  carrot  tops,  and  weld,  have  been  tried,  but  without 
advantage,  with  the  exception,  perhaps,  of  weld,  which  is  still 
used  by  some  dyers.     Some  chemists  regard  the  use  of  wroad  as 


NOTES  UPON  INDIGO. 


39 


the  remnant  of  a  prejudice  ;  but  the  better  opinion  is,  that  this 
material  possesses  peculiar  fermentiscible  qualities,  whose  exact 
action  science  has  yet  to  resolve. 

According  to  Schutzenberger,  the  most  recent  and  highest 
French  authority,  the  dimensions  of  the  pastel  vat  are  about  6J- 
feet  in  diameter,  by  9  in  depth.  100  kilograms  (221  lbs.)  of 
pastel,  in  balls,  is  placed  in  the  vat,  which  is  then  filled  with 
boiling  water.  To  this  is  added  10  kilograms  (22  lbs.)  of  mad- 
der, 3  to  4  kilograms  (about  6§  to  8|  lbs.)  of  bran,  and  4 
kilograms  of  quicklime,  which  has  been  slacked,  and  in  the  form 
of  a  bouilli.  Sometimes  weld  is  also  added.  After  three  hours 
of  rest,  the  vat  is  well  raked,  and  the  operation  is  repeated  every 
three  hours.  There  is  gradually  developed  a  characteristic  am- 
moniacal  vapor,  and  a  blue  scum,  with  veins  of  deeper  blue, 
forms  on  the  surface ;  and  the  liquid,  when  agitated  in  the  air, 
rapidly  becomes  blue.  These  symptoms  indicate  the  dissolution 
of  the  indigotine  of  the  woad  ;  then  there  is  added  10  kilograms 
(22  lbs.)  of  indigo  which  has  been  previously  ground  in  water, 
and  the  vat  is  stirred.  If  the  fermentation  appears  to  be  pro- 
ceeding too  actively,  which  is  recognized  by  the  disengagement 
of  gases,  it  is  checked  by  the  addition  of  a  proper  dose  of  lime. 
On  the  other  hand,  the  fermentation  is  made  more  active  by 
increasing  the  dose  of  bran.  The  first  dyes  are  not  so  good  as 
those  subsequently  obtained,  as  the  woad  absorbs  from  the  bath 
certain  brown  or  yellow  materials,  kept  in  solution,  and  fur- 
nished as  well  by  the  pastel  and  madder  as  by  the  indigo  itself. 
100  kilograms  of  wool  require  from  8  to  12  kilograms  of 
indigo.  The  vat  is  kept  up  by  successive  additions  of  indigo 
and  lime,  made  in  the  evening. 

Another  kind  of  pastel  vat,  prepared  much  like  the  last, 
receives  an  addition  of  a  dose  of  potash.  M.  de  Kaeppelin  de- 
scribes it  as  the  one  at  present  in  general  use  in  France.  Into 
a  vat  containing  from  3,000  to  4,000  litres  (791  to  1,055  gallons) 
there  is  placed  75  kilograms  (166  lbs.)  of  pastel  in  loaves,  or 
which  has  undergone  a  kind  of  fermentation  ;  or,  what  is  prefer- 
able, 80  to  100  kilograms  (176  to  221  lbs.)  of  pastel  or  woad 
gathered  without  fermentation,  and  10  kilograms  (22  lbs.)  of 


40 


NOTES  UPON  INDIGO. 


indigo,  ground  to  a  paste  with  water.  This  mixture  is  well 
stirred,  and  there  is  added  4  kilograms  (about  9  lbs.)  of  Avig- 
non madder,  and  the,  same  quantity  of  carbonate  of  potash. 
After  the  vat  has  been  well  raked  there  is  added  2  kilograms 
(4J  lbs.)  of  slacked  lime,  and  some  pails  of  bran.  The  vat  is 
well  covered,  either  with  a  wooden  lid,  or  woollen  cloths.  The 
fermentation  is  allowed  to  proceed,  and  after  five  or  six  hours 
the  vat  is  uncovered  and  raked  with  much  care  for  half  an  hour. 
This  operation  is  repeated  every  three  hours,  until  it  is  recog- 
nized that  the  indigo  is  well  dissolved.  In  this  case  the  bath 
ought  to  be  of  a  beautiful  yellow  color,  and  be  covered  with  a 
light  blue  irised  film,  veined  with  yellow  at  the  least  movement 
given  to  the  liquid.  If  the  fermentation  proceeds  too  rapidly,  a 
little  lime  is  added  to  moderate  it. 

For  keeping  up  a  vat  like  this,  and  to  obviate  the  different 
inconveniences  to  which  it  is  subject,  the  dyer  sometimes  adds 
lime,  or  sugar,  and  carbonate  of  ammonia,  sometimes  madder,  or 
bi*an,  or  even  tartar-lees.  These  last  additions  are  made  to  satu- 
rate the  excess  of  lime  which  the  vat  contains.  In  this  case  the 
yellow  veins  and  the  beautiful  blue  scum  which  cover  the  surface 
disappear,  or  become  pale  ;  a  piquant  odor  is  disengaged,  and 
the  liquor  becomes  blackish.  When  lime  or  sugar  are  added,  it 
is  for  the  purpose  of  retarding  the  fermentation  of  the  woad. 
Sugar  might  even  entirely  take  the  place  of  pastel  for  effecting 
the  reduction  of  the  indigo,  and  many  establishments  in  France 
are  commencing  to  use  it  for  this  purpose.  A  good  vat,  well 
supplied  with  successive  additions  of  indigo,  pastel,  bran,  and 
madder,  in  proportions  necessary  to  effect  and  prolong  the  fer- 
mentation necessary  for  the  dissolution  of  the  indigo,  may  be 
kept  up  many  years. 

Schutzenberger  observes  that  the  vats  of  fermentation  are 
subject  to  certain  maladies,  the  two  most  frequent  of  which  are 
due,  one  to  an  excess,  and  the  other  to  an  insufficient  quantity 
of  lime.  "  In  the  first  case,  the  liquid  takes  a  tint  more  and  more 
free  of  color,  loses  its  fleuree  (surface  scum)  and  odor  ;  the  fer- 
mentation is  then  arrested  by  the  precipitation  of  the  active 
matters.    This  inconvenience  is  remedied,  if  seen  in  time,  by 


NOTES  UPON  INDIGO. 


41 


adding  sulphate  of  iron,  which  eliminates  the  too  great  excess 
of  lime.  In  the  second,  the  fermentation  becomes  too  active, 
passes  into  a  putrid  fermentation,  and  the  liquid  assumes  a 
reddish  tint ;  a  fabric  dyed  with  indigo  in  this  state  becomes 
very  soon  discolored.  The  sole  means  of  safety  is  to  heat  the 
bath  up  to  90°  and  to  add  lime.  If  this  does  not  accomplish 
the  purpose  of  arresting  the  putrefaction  the  vat  is  lost." 

The  following  account  of  the  method  of  dyeing  w.oollen  goods 
with  indigo  by  means  of  the  woad  vat  is  given  by  Dr.  Ure,  as 
that  carried  on  in  Yorkshire,  the  great  centre  of  the  woollen 
manufacture  of  England. 

"  The  dye-vats  employed  are  circular,  having  a  diameter  of 
six  feet  six  inches,  and  depth  of  seven  feet,  and  are  made  of  cast- 
iron  five-eighths  of  an  inch  in  thickness.  They  are  surrounded 
by  brickwork,  a  space  of  three  inches  in  width  being  left  be- 
tween the  brickwork  and  the  iron,  for  the  purpose  of  admitting 
steam,  by  means  of  which  the  vats  are  heated.  The  interior 
surface  of  the  brickwork  is  well  cemented.  In  setting  a  vat 
the  following  materials  are  used  :  5  cwt.  of  woad,  30  lbs.  of 
indigo,  56  lbs.  of  bran,  7  lbs.  of  madder,  10  quarts  of  lime. 
The  woad  supplied  to  the  Yorkshire  dyers  is  grown  and  pre- 
pared in  Lincolnshire.  It  is  in  the  form  of  a  thick,  brownish 
yellow  paste,  having  a  strong  ammoniacal  smell.  The  indigo  is 
ground  with  water  in  the  usual  manner.  The  madder  acts  in 
promoting  fermentation,  but  it  also  serves  to  give  a  reddish 
tinge  to  the  color.  The  lime  is  prepared  by  putting  quicklime 
into  a  basket,  then  dipping  it  in  water  for  an  instant,  lifting  it 
out  again,  and  then  passing  it  through  a  sieve,  by  which  means 
it  is  reduced  to  a  fine  powder,  called  by  the  dyers  ware.  The 
vat  is  first  filled  with  water,  which  is  heated  to  140°  F.,  after 
which  the  materials  are  put  in,  and  the  whole  is  well  stirred  until 
the  woad  is  dissolved  or  diffused,  and  it  is  then  left  to  stand 
undisturbed  overnight ;  at  six  o'clock  the  next  morning  the 
liquor  is  again  stirred  up,  and  five  quarts  more  of  lime  are  added  ; 
at  ten  o'clock  five  pints  of  lime  are  again  thrown  in,  and  at 
twelve  o'clock  the  heat  is  raised  to  120°  F.,  which  temperature 
must  be  kept  up  until  three  o'clock,  when  another  quart  of  lime 

6 


42 


NOTES  UPON  INDIGO. 


is  introduced.  The  vat  is  now  ready  for  dyeing.  When  the 
process  of  fermentation  is  proceeding  in  a  regular  manner,  the 
liquid,  though  muddy  from  insoluble  vegetable  matter  in  suspen- 
sion, is  of  a  yellow  or  olive  yellow  color ;  its  surface  is  covered 
with  a  blue  froth  or  copper-colored  pellicle,  and  it  exhales  a 
peculiar  ammoniacal  odor ;  at  the  bottom  of  the  vat  there  is  a 
mass  of  undissolved  matter  of  a  dirty  yellow  color.  If  there  is 
an  excess  of  lime  present,  the  liquor  has  a  dark  green  color,  and 
is  covered  with  a  grayish  film,  and,  when  agitated,  the  bubbles 
which  are  formed  agglomerate  on  the  surface,  and  are  not  easily 
broken.  Cloth  dyed  in  a  liquid  of  this  kind  loses  its  color  on 
being  washed.  This  state  of  the  vat  is  remedied  by  the  addition 
of  bran,  and  is  of  no  serious  consequence .  When,  on  the  other 
hand,  there  is  a  deficiency  of  lime,  or,  in  other  words,  when  the 
fermentation  is  too  active,  the  liquor  acquires  first  a  drab,  then 
a  clay-like  color ;  when  agitated,  the  bubbles  which  form  on  its 
surface  burst  easily,  and  when  stirred  up  from  the  bottom  with 
a  rake  it  effervesces  slightly,  or  frits,  as  the  dyers  say.  If  the 
fermentation  be  not  checked  at  this  stage,  putrefaction  soon  sets  in, 
the  liquid  begins  to  exhale  a  fetid  odor,  and  when  stirred  evolves 
large  quantities  of  gas,  which  burns  with  a  blue  flame  on  the 
application  of  a  light.  The  indigo  is  now  totally  destroyed, 
and  the  contents  of  the  vat  may  be  thrown  away.  No  further 
addition  of  woad  is  required  after  the  introduction  of  the  quan- 
tity taken  in  first  setting  the  vat,  the  fermentation  being  kept  up 
by  adding  daily  about  four  pounds  of  bran  with  one  quart  or  three 
quarts  of  lime.  Indigo  is  also  added  daily  for  about  three  or 
four  months.  The  vat  is  then  used  for  the  purpose  of  dyeing 
light  shades,  until  the  indigo  contained  in  it  is  quite  exhausted, 
and  its  contents  are  then  thrown  away." 

This  author  adds  :  "  Woollen  cloth,  before  being  dyed,  is  boiled 
in  water  for  one  hour,  then  passed  immediately  under  cold  water. 
If  it  be  suffered  to  lie  in  heaps  after  being  boiled  it  undergoes 
some  change,  which  renders  it  afterwards  incapable  of  taking  up 
color  in  the  vat.  In  dyeing,  the  cloth  is  placed  on  a  net-work 
of  rope  attached  to  an  iron  ring,  which  is  suspended  by  four 
iron  chains  to  a  depth  of  about  three  feet  beneath  the  surface  of  the 


NOTES  UPON  INDIGO. 


43 


liquor.*  The  cloth  is  stirred  about  in  the  liquor  by  means  of 
hooks  for  about  twenty  or  thirty  minutes.  It  is  then  taken  out 
and  well  wrung,  It  now  appears  green,  but,  on  being  unfolded 
and  exposed  to  the  air,  rapidly  becomes  blue.  When  the  vat  has 
an  excess  of  lime  the  cloth  has  a  dark  green  color  when  taken 
out.  It  is  then  passed  through  hot  water,  and  dipped  again  if  a 
darker  shade  is  required. 

The  Indian  Vat.  — This  presents  much  analogy  to  the  woad 
vat,  as  the  fermentation  of  vegetable  matters  effects  the  transfor- 
mation of  the  indigo-blue.  According  to  Dr.  Calvert,  the  Indian 
vat,  probably  so  called  from  its  origin  in  the  East,  is  taking  the 
place  in  England  of  the  old  woad  vat  for  dyeing  wool  and  wool- 
lens. He  describes  its  preparation  as  follows  :  8  lbs.  of  powdered 
indigo  is  added  to  a  bath  containing  3  J  lbs.  of  bran,  3^  lbs.  of 
madder,  and  12  lbs.  of  potash,  which  is  maintained  for  several 
hours  at  a  temperature  of  200°  F.  It  is  then  allowed  to  cool  to 
100°  F. ,  when  fermentation  ensues.  After  about  forty-eight  hours 
the  indigo  is  rendered  soluble,  being  reduced  by  the  decomposi- 
tion of  the  sugar  and  other  products  contained  in  the  bran  and 
the  madder  root  during  the  process  of  fermentation.  The 
distinguishing  feature  of  this  vat  is  the  use  of  potash.  The 
Indian  or  potash  vats  are  spoken  of  by  the  best  authorities  as  more 
easy  to  manage  than  the  woad  vat.  They  are  less  subject  to 
accidents,  and  yield  #their  coloring  material  more  readily  to  the 
fibre,  while  three  times  as  much  wool  can  be  dyed  in  the  same 
time.  On  the  other  hand,  they  do  not  last  so  long,  and  require 
to  be  renewed  at  the  end  of  twenty-five  or  thirty  days.  Besides, 
the  fibres  dyed  in  the  potash  vat  have  a  darker  shade  than  those 
dyed  in  the  woad  vat,  owing  to  the  large  quantity  of  the  coloring 
matter  of  the  madder  dissolved  by  the  potash,  which  becomes 
fixed  on  the  stuff  with  the  indigo-blue. 

The  Urine  Vat,  but  little  used  except  for  domestic  dyeing,  is 
founded  upon  the  same  principles  as  the  other  fermenting  vats. 
This  excretion,  when  putrefied,  contains  at  the  same  time  the 
nitrogenized  principles  which  work  as  ferments  and  the  alkali 
in  the  form  of  ammonia  necessary  for  dissolving  the  indigo. 

According  to  Dr.  Calvert,  improvements  have  been  made  of 


44 


NOTES  UPON  INDIGO. 


late  years  in  the  fermenting  indigo  vats  by  which  the  expense 
of  madder  is  avoided.  They  are  now  prepared  by  adding  to 
water,  at  a  temperature  of  200°  F.,  2  buckets  of  bran,  26  lbs. 
of  soda  crystals,  12  lbs.  of  indigo,  and  5  lbs.  of  slacked  lime. 
After  five  hours  the  bath  is  allowed  to  cool  to  100°  F.,  when 
fermentation  ensues,  and  the  indigo  is  dissolved  in  the  alkali. 
This  is,  in  fact,  the  German  vat,  soda  taking  the  place  of  the 
potash,  and  the  only  fermenting  material  consisting  of  bran. 

The  German  Vat  is  largely  used  by  the  dyers  in  the  north  of 
France,  and  is  considered  as  more  advantageous  than  the 
Indian  vat,  because  the  employment  of  soda  is  more  economical 
than  that  of  potash,  while  the  vat  can  be  maintained  as  long  as 
two  years.  The  vats  used  by  them  are  prepared  as  follows  : 
The  water  is  heated  to  a  temperature  of  95°,  and  receives  20 
pails  of  bran,  11  kilograms  (about  24  lbs.)  of  crystals  of 
carbonate  of  soda,  5.5  kilograms  (11  lbs.)  of  indigo,  and  4J 
lbs.  of  slacked  lime.  After  twelve  hours,  the  temperature  hav- 
ing been  kept  at  40°  or  50°,  fermentation  commences,  the  liquid 
becomes  of  a  greenish  blue  color,  and  disen^a^es  bubbles  of  £as. 
Indigo,  soda,  and  lime  are  put  in  from  time  to  time  in  the  pro- 
portions above  indicated,  and  also  from  six  to  eight  pounds  of 
molasses.    At  the  end  of  the  third  day  the  vat  is  fit  for  use. 

M.  de  Kseppelin,  writing  in.  1864,  informs  us  that  the  reduc- 
tion of  indigo  by  means  of  molasses,  is  at%  present  largely  em- 
ployed in  the  great  establishments  for  dyeing  woollen  cloth  at 
Sedan,  Louviers,  and  Elboeuf. 

The  vat  used  is  of  very  large  dimensions,  and  from  twenty- 
two  to  twenty-six  pounds  of  indigo  are  dissolved  in  it ;  an  equal 
weight  of  molasses  is  used,  and  three  or  four  times  the  same 
weight  of  potash  made  caustic  by  a  proportionate  addition  of  lime. 

The  space  reserved  for  this  subject  in  our  present  paper  will 
not  permit  us  to  enter  upon  a  description  of  the  processes  used 
in  the  American  dye-houses.  This,  as  well  as  the  applications 
of  indigo  in  printing,  and  the  uses  of  sulphate  of  indigo,  must  be 
deferred  to  another  number. 

Let  us,  in  concluding  the  first  part  of  our  paper,  at  the  risk  of 


NOTES  UPON  INDIGO. 


45 


repetition,  bring  out  in  bolder  relief  a  statement  which  presents 
the  philosophy  of  all  the  various  processes  of  the  indigo  vat, 
and  at  the  same  time,  a  conclusive  argument  for  the  use  of  this 
materia],  in  preference  to  all  cheaper  substitutes.  Indigo  can- 
not enter  into  a  fibre  until  it  is  dissolved.  It  cannot  be  dis- 
solved so  long  as  it  is  in  a  blue  state.  When  reduced  by  any 
of  the  processes  above  described  to  the  white  state,  it  is  easily 
dissolved,  and  can  enter  the  pores  of  the  fibre.  Upon  exposure 
to  the  oxygen  of  the  air  it  takes  up  an  equivalent  of  oxy- 
gen ;  it  returns  to  the  blue  state,  and,  being  then  insoluble,  it 
cannot  be  washed  away  from  the  fabric,  and  being  saturated  with 
oxygen  it  cannot  be  changed  by  air  or  light.  This  theory  of 
the  application  of  indigo  involves  a  lesson  to  manufacturers, 
dealers,  and  consumers,  especially  of  woollen  fabrics.  The 
theory,  as  well  as  experience,  dating  back  to  the  dawn  of 
the  textile  arts  in  the  East,  establishes  that  this  material  is  in- 
calculably superior  to  any  other,  in  permanence  at  least,  for 
imparting  to  woollen  fibre  a  blue  color,  or  as  a  foundation 
for  most  of  the  darker  colors.  By  far  the  largest  proportion 
of  all  cloths  are  of  dark  colors,  —  blue,  black,  green,  brown,  gray, 
or  mixed,  —  and  can  advantageously  receive  in  all  or  a  portion  of 
the  fibre  constituting  them  a  direct  dye  or  bottom  for  other  dyes 
from  indigo.  It  may  be  safely  stated  that,  as  a  whole,  no 
cloths  in  the'world  are  manufactured  from  such  good  wool  as  those 
produced  in  the  United  States.  We  might  expect  that  the 
shoddy  goods  of  Yorkshire  should  be  further  falsified  by  fuga- 
cious dyes  ;  but  is  it  not  a  shame  that  our  admirable  wool 
should  be  deprived  of  half  its  value  by  parsimony  in  dyeing? 
The  slightest  shortcomings  in  dyeing  are  revealed  in  wrear.  The 
writer  cannot  forbear  referring  to  an  illustration'  directly  before 
his  eyes.  He  is  wearing  a  garment,  reduced  now  to  the  retired 
service  of  an  office  coat,  made  of  an  admirable  cheviot  cloth 
of  American  manufacture.  The  cloth  originally  was  selected 
not  only  for  its  excellent  texture,  but  as  an  illustration  of 
philosophical  principles  applied  in  the  formation  of  color.  The 
tissue  was  made  by  weaving  three  yarns  of  distinct  colors,  —  blue, 
yellow,  and  red.    Either  of  those  hues  alone  would  have  been 


46 


NOTES  UPON  INDIGO. 


glaring  and  conspicuous,  but,  by  the  law  of  color,  the  combi- 
nation of  blue,  red,  and  yellow  makes  black,  and  the  new 
cloth  at  a  distance  had  the  effect  of  a  dark  mixture.  Upon  ex- 
posure to  ordinary  wear,  the  yellow  and  red  have  retained 
their  pristine  hues  ;  the  blue,  not  being  indigo  dyed,  has  faded ; 
and  the  original  dark  mixture,  although  sound  in  fabric,  has 
become  of  a  yellowish  brown.  The  extra  expense  of  a  permanent 
dyeing  material  forms  so  small  a  proportion  of  the  whole  cost  of  a 
finished  garment,  that  it  ought  not  to  be  generally  spared.  The 
reform  cannot  be  made  by  the  manufacturers  ;  it  must  be  made  by 
the  dealers,  and  especially  by  that  class  of  producers  which  has 
risen  in  our  day  into  such  great  importance,  — the  manufacturers 
of  ready-made  clothing.  If  they  would  demand  of  the  manu- 
facturers, and  furnish  to  their  customers  cloths  more  permanently 
dyed,  it  would  be  another  step  in  the  direction  to  which  these 
establishments  are  tending,  — the  supply  of  the  chief  portion  of 
the  woollen  clothing  of  the  people.  The  manufacturers  would 
gladly  aid  them  ;  for  it  is  the  growing  sentiment  of  American 
manufacturers  that  all  their  productions  should  be,  in  the  pro- 
verbial phrase  adopted  from  the  dye-house,  as  expressing  the 
highest  excellence,  —  true  blue. 


BIBLIOGRAPHY. 


Citations  of  authorities  having  been  but  partially  made  in  the  preceding 
article,  the  writer,  for  the  purpose  of  giving  his  sources  of  information,  and 
for  the  convenience  of  those  who  wish  to  pursue  the  subject  further,  appends 
a  list  of  the  more  important  works  which  he  has  consulted  :  — 

Schutzenberger's  Traite  des  Matieres  Colorantes,  t.  ii.  (the  most  recent 
and  best  modern  authority)  ;  Bancroft's  Philosophy  of  Permanent  Colors, 
vol.  i. ;  Edinburgh  Encyclopaedia  ;  Berzelius,  Traite  de  Chimie,  t.  vi ;  Chev- 
rueil,  Lemons  de  Chimie  Appliquee  a  Teinture,  t.  iii. ;  Dumas,  Chimie  Appli- 
quee aux  Arts,  t.  viii ;  Wurtz,  Dictionnaire  de  Chimie,  1872,  art.  Indigo ; 
Indigo  et  son  Emploi,  par  De  Kseppelin  ;  Annales  du  Genie  Civil,  1864,  t.  iii. ; 
Lectures  of  Dr.  Grace  Calvert,  Chemical  News,  Aug.  9  and  23,  1872 ; 
O'Neill's  Dictionary  of  Dyeing  and  Printing  ;  Napier's  Chemistry  Adapted  to 
Dyeing ;  Muspratt's  Chemistry  Applied  to  the  Arts,  articles  Indigo  and  Dye- 
ing; Ure's  Dictionary  of  Manufactures,  ed.  of  1860;  Proceedings  of  Royal 
Society,  vol.  xvi. ;  Proceedings  of  Literary  and  Philosophic  Society  of  Man- 
chester, vol.  iv. ;  McCulloch's  Dictionary  of  Commerce,  ed.  1869 ;  Diction- 
naire Universel  du  Commerce,  &c,  ed.  1861 ;  South  Carolina  Production  . — 
Ramsay's  History  ;  Drayton's  South  Carolina  ;  Silliman's  Journal,  vol.  xviii. 
A  more  complete  bibliography  is  gi^en  in  Schutzenberger's  work. 


PART  II. 


PAET  II. 


We  entered  upon  the  subject  of  indigo,  which  we  have  treated 
at  some  length  in  our  last  issue,  as  much  in  the  interest  of 
the  people  as  of  manufacturers,  for  we  were  deeply  impressed 
with  the  conviction  that  no  improvement  in  our  manufacturing 
processes  would  confer  more  benefit  upon  the  masses  than  impart- 
ing stability  of  color  to  the  clothing  of  the  people.  When  one  has 
a  deep  conviction  upon  a  subject,  upon  which  others  have  equal 
opportunities  for  judging,  he  may  be  sure  that  he  is  not  alone  in 
his  impressions.  He  is  moved  by  one  of  those  waves  of  thought 
which,  operating  simultaneously  upon  many  minds,  gives  that 
uniformity  to  public  opinion  at  which  we  so  often  wonder.  We 
are  gratified  to  find,  from  responses  to  our  last  article,  that  we 
are  not  alone  in  our  conviction  of  the  importance  of  reviving 
"true  blue  99  dyes.  The  head  of  a  mercantile  house,  the  extent 
of  whose  clientele  in  mills  both  of  wool  and  cotton  is  hardly 
surpassed,  has  assured  us  that  we  have  not  overstated  the  reform 
in  dyeing  which  we  have  advocated.  He  had  long  shared  in 
our  convictions.  Pointing  to  the  throng  of  men  in  the  crowded 
street,  where  we  were  conversing,  he  remarked  that  there  was 
hardly  a  man  in  the  crowd  whose  clothing  would  not  have  been 
improved  by  indigo  dye.    "  The  failure  to  use  indigo  dyes,"  he 


52 


NOTES  UPON  INDIGO. 


emphatically  said,  "  costs  the  laboring  people  of  this  country  mil- 
lions of  dollars  every  year.  The  fault  is  not  to  be  charged  to  our 
own  manufacturers  alone ;  for  the  blue  coat  which  I  wear,  and 
which  I  bought  in  Paris,  annoys  me  by  the  crocking  caused  by 
its  aniline  dye."  In  one  very  large  mill  of  which  he  is  director 
as  well  as  selling  agent,  he  is  putting  his  principles  in  practice. 
All  the  heavy  blue  cloths  intended  for  popular  consumption 
are  faithfully  dyed,  and  each  bears  a  stamp,  "  Warranted  indigo 
dyed."  The  ready-made  clothing  establishments  which  largely 
consume  these  goods  have  already  found  their  advantage  in  pur- 
chasing them,  and  a  similar  stamp  is  attached  to  each  article 
made  from  this  cloth. 

Some  of  our  most  celebrated  cotton  fabrics  have  won  and 
still  retain  their  reputation  by  the  use  of  indigo  dyes.  The 
ginghams  are  a  signal  illustration.  The  blue  check  is  formed 
by  weaving  cotton  yarns  dyed  blue  in  the  cold  indigo  vat  with 
undyed  yarns.  These  goods  can  be  washed  indefinitely  without 
change. 

Another  illustration  is  the  famous  A.  B.  A.  Amoskeag  tickings, 
an  article  of  such  excellence  that  the  question  of  the  right  to 
use  trade-mark  A.  B.  A.  gave  rise  to  the  leading  American  case 
in  this  branch  of  law.*  A  prominent  feature  in  these  goods 
was  and  still  is  the  permanence  of  the  dye  in  the  blue  stripe, 
produced  by  the  cold  indigo  vat.  Still  another  illustration  is 
the  blue  and  white  "  shirting  stripe  w  first  made  by  Mr.  Samuel 
Batchelder,  at  the  Hamilton  Mills,  now  so  generally  adopted 
for  sailors'  shirts.  The  indigo  dye  enables  the  color  to  resist  the 
roughest  possible  usage. 

To  recur  to  the  application  of  indigo  dyeing  to  wool  and 
woollens.  We  have  been  unable,  although  we  have  written 
more  than  fifty  letters  of  inquiry  upon  the  subject,  to  learn  of 
any  peculiarity  or  improvements  in  the  American  processes  of 
wool  dyeing  with  indigo,  f    Our  dyers  are  for  the  most  part  for- 


*  See  the  case  stated  at  length  in  our  article  on  Trade-marks,  Bulletin,  vol.  i.  p.  102. 

t  A  reply  by  Mr.  D.  R.  Whitney,  an  extensive  indigo  importer,  to  a  letter  of  inquiry, 
enables  us  to  correct  some  errors  in  our  former  article,  under  the  head  of  "  commerce 
in  indigo."    The  value  of  export  from  India  in  1862-63,  stated  in  dollars,  through  a 


NOTES  UPON  INDIGO. 


53 


eigners.  For  this  reason,  or  because  the  art  of  indigo  dyeing  has 
long  since  reached  perfection  in  the  best  establishments  abroad, 
they  rigidly  pursue  the  old  European  methods.  The  best  dyers 
regard  the  successful  management  of  the  warm  fermenting  vats 
for  wool  as  the  highest  test  of  their  art.  We  have  already 
spoken  of  the  complicity  of  the  phenomena  in  fermentations. 
Practical  dyers  endow  the  fermenting  vat  with  a  sort  of  per- 
sonality. "An  indigo  vat,"  says  one  to  us,  "is  more  like  a  sick 
man  than  any  thing  in  the  world  :  you  have  to  watch  it  as  you 
would  a  sick  patient,  and  give  it  physic  or  ferments  to  stir  up 
the  system  and  purify  it."  *  The  diagnosis  of  a  sick  vat  requires 
that  sort  of  instinctive  knowledge  which  experience  gives  to  the 
practised  physician.  The  impatience  of  our  young  Americans 
will  not  permit  them  to  serve  the  long  apprenticeship  necessary 
to  acquire  the  proper  experience.  The  artisans  not  thoroughly 
trained  will  naturally  prefer  the  dyes  and  processes  introduced 
by  modern  science,  which  require  but  little  skill  in  their  appli- 
cation. It  is  a  curious  fact  that  the  influence  of  the  national 
government  has  been  largely  instrumental  in  preserving  the 
old  system  of  indigo  dyeing.  Thanks  to  the  Quartermaster- 
General's  Bureau,  or  the  man  of  science,  General  Meigs,  who 
presides  over  it,  indigo  dyed  cloths  have  been  persistently  in- 
sisted upon  for  the  army.  The  late  war  gave  a  new  impulse  to 
indigo  dyeing.  A  skilled  dyer,  whom  we  have  consulted,  was 
constantly  employed  in  Connecticut,  on  a  tour  of  professional 
inspection  of  a  dozen  or  more  different  establishments  making 
army  goods.  No  doctor,  he  says,  ever  found  in  hospital  prac- 
tice more  complications  of  disease  than  he  found  in  the  ail- 


typographical  error,  should  have  been  pounds  sterling  ;  thus,  instead  of  $2,126,814,  read 
.£2,126,814.  It  is  stated  in  our  first  article  that  the  telegrams  show  a  decline  of  price 
of  indigo  in  the  Indian  trade  of  from  50  to  75  per  cent;  "per  cent"  should  read 
"  rupees,"  which  would  make  a  decline  of  from  25  to  30  per  cent.  The  reason  for  the 
decline,  as  stated  by  Mr.  Whitney,  is  the  unusually  large  crop  of  this  year.  The  average 
crop  of  indigo  in  Bengal  is  about  100,000  maunds.  The  crop  of  this  year  is  135,000 
maunds,  about  30  to  35  per  cent  above  the  average. 

According  to  Mr.  Whitney,  the  consumption  of  Bengal  indigo  in  the  United  States 
was  2,458  cases  of  270  lbs.  to  a  case  on  an  average,  in  1871;  and  in  1872,  1,802  cases. 
Guatemala  indigo,  3,132  serroons  in  1871,  and  2,578  serroons  in  1872. 

*  See  notes  on  "  sickness  "  of  vats  in  Appendix. 


54 


NOTES  UPON  INDIGO. 


ing  vats.  Among  other  difficulties  there  was  a  deficiency  of 
imported  woads,  although  the  cultivation  of  excellent  woad 
immediately  sprung  up  in  Connecticut.  In  the  mean  time  carrot 
and  rhubarb  tops  were  used  as  substitutes  for  the  fermenting 
material  of  the  woad.  Carrot-tops  grown  expressly  for  that 
purpose  brought  as  high  as  twenty-five  cents  per  pound.  Since 
the  war  the  requisitions  for  indigo-dyed  woollen  goods  have  not 
relaxed,  and  the  art  is  not  likely  to  be  lost. 

With  the  real  difficulties  which  attend  the  process,  it  is  hard 
for  indigo  dyeing  to  sustain  itself  in  the  face  of  cheap  substitutes 
of  easy  application,  such  as  the  Nicholson  blue.  It  is  exceed- 
ingly difficult  to  piece  dye  with  indigo  and  preserve  a  uniform 
hue  upon  the  cloth.  Hence  indigo  dyes  are  generally  given  in 
the  wool.  The  wool  absorbing  the  foreign  material  of  the  dye 
is  more  difficult  to  work  in  the  operations  of  carding  and  spin- 
ing.  In  other  words,  a  finer  and  costlier  wool  is  required.  A 
great  desideratum  therefore  is  a  means  of  piece  dyeing  with 
indigo  so  as  to  preserve  a  perfect  uniformity  of  hue  throughout  the 
piece.  This,  we  are  happy  to  say,  has  been  recently  successfully 
accomplished  by  one  of  the  largest  and  most  faithful  of  our  cloth- 
making  establishments.  It  would  be  premature,  before  the 
patents  are  secured  for  this  invention,  to  explain  the  ingenious 
and  expensive  apparatus  devised  for  this  purpose,  which  con- 
stitutes in  fact  a  battery  of  vats  so  arranged  that  the  operation 
may  be  continuous.  The  experiments  authorize  the  statement 
that  bottom  dyes  of  indigo,  so  desirable  for  a  great  variety  of 
colors,  can  be  applied  with  no  other  additional  cost  than  that  of 
the  dyeing  material.  When  this  establishment,  as  it  proposes, 
stamps  upon  the  cards  which  designate  goods,  already  so  admi- 
rable in  material  and  texture,  "  Warranted  indigo  dyed,"  we 
shall  regard  it  as  an  era  in  the  American  card-wool  manu- 
facture. 

The  old  European  woad  vat  process  is  that  used  in  all  our 
establishments.  Mr.  Henderson  of  the  Washington  Mills,  whose 
experience  as  a  practical  dyer  of  wool  is  exceptionally  large, 
informs  us  that  he  has  found  no  work  so  instructive  upon  this 
process  as  Napier's  "Chemistry  of  Dyeing  "  (published  by  Henry 


NOTES  UPON  INDIGO. 


55 


Carey  Baird,  of  Philadelphia,  1869).  Napier's  description  of 
the  process  is  extracted  from  Dumas's  "Lectures  on  Dyeing." 
The  appreciation  expressed  by  so  competent  a  judge  induces  us 
to  reprint  Dumas'  description  in  an  appendix  to  this  article. 

That  we  may  give  at  least  a  general  view  of  the  whole  subject, 
we  will  proceed  to  consider  indigo  in  some  relations  not  yet 
adverted  to. 

In  Part  I.  of  our  notes  we  have  treated  only  of  the  applica- 
tion of  this  substance  in  dyeing  by  means  of  reduction  through 
the  indigo  vat.  Indigo  may  be  applied  by  means  of  reduction 
in  the  printing  of  fabrics,  as  well  as  in  dyeing  them.  A  true 
scientific  arrangement  would  compel  us  next  in  order  to  consider 
this  other  application  of  indigo  by  means  of  reduction.  But  the 
more  natural  and  practical  order  is  to  pursue  the  subject  of 
dyeing,  and  to  consider  next  the  applications  of  the  derivatives 
from  indigo  in  dyeing  proper. 

SULPHURIC  DERIVATIVES, — SAXON  BLUE,  &C. 

The  powerful  action  of  sulphuric  acid  upon  indigo,  and  the 
bright  and  lively  blue  color  thereby  produced,  had  been  ob- 
served by  chemists  long  ago ;  but  no  person  appears  to  have 
applied  this  color  upon  cloth,  until  it  was  done  about  the  year 
1740,  by  Counsellor  Barth,  at  Grossenhein,  in  Saxony.  The 
vividness  of  the  dye,  and  the  facility  with  which  it  was  applied, 
brought  it  into  great  vogue  under  the  name  of  Saxon  blue,  from 
its  origin.  Its  popularity  in  former  times  is  evinced  by  the 
words  of  the  old  song,  "  The  Blue  Bells  of  Scotland  :  "  — 

"  In  what  clothes,  in  what  clothes  is  your  Highland  laddie  clad  ? 
His  bonnet's  of  the  Saxon  blue,  his  waistcoat  of  the  plaid."  *  ^ 

The  Saxon  blue  consists  simply  of  a  solution  of  indigo,  the 
Guatemala  blue  indigo  being  preferred,  in  sulphuric  acid  suitably 
diluted  with  water.  The  result  of  this  reaction  is  not  a  single 
chemical  substance,  but  two  acids  giving  different  tints,  one 
called  sulpho-purpuric  acid  or  phenicine,  and  the  other  sulpho- 
indigotic  acid ;  the  first  giving  to  wool  a  reddish-violet  color, 

*  First  sung  by  Mrs.  Jordan,  about  the  year  1799. 


56 


NOTES  UPON  INDIGO. 


and  the  other  a  pure  blue.  A  third  compound  has  been  indicated 
by  Berzelius,  the  nature  of  which  has  not  been  determined. 
Whether  one  or  the  other  of  the  two  named  acids,  or  the  two 
combined,  shall  be  produced  by  the  reaction  between  the  sul- 
phuric acid  and  the  indigo,  depends  upon  the  duration  of  the 
contact,  the  temperature  of  the  mixture,  and  the  nature  and 
proportion  of  the  acid  used. 

Persoz  gives  the  following  general  receipt :  — 

' '  1  part  by  weight  of  indigo,  finely  rubbed. 
1    „    „       „     „  Nordhaussen  acid. 
1    „    „       „     „  ordinary  sulphuric  acid. 

Leave  for  forty-eight  hours,  then  heat  until  a  drop  turned  into 
water  will  dissolve  without  producing  a  precipitate.  Leave  to 
cool,  and  dilute  with  water  till  the  strength  is  brought  to  18 
Beaume." 

Napier  says  that  he  has  found  the  following  method  of  pre- 
paring sulphate  of  indigo,  in  quantities  for  use,  very  satisfactory  : 
"  The  indigo  is  reduced  to  an  impalpable  powder,  and  com- 
pletely dried  by  placing  it  on  a  sand  bath  or  flue  for  some  hours 
at  a  temperature  of  about  150°  F.  For  each  pound  of  indigo 
six  pounds  of  highly  concentrated  sulphuric  acid  are  put  into  a 
large  jar,  or  earthen  pot,  furnished  with  a  cover.  This  is  kept 
in  as  dry  a  place  as  possible,  and  the  indigo  is  added  gradually 
in  small  quantities.  The  vessel  is  kept  closely  covered,  and 
care  taken  that  the  heat  of  the  solution  does  not  exceed  212°  F. 
When  the  indigo  is  all  added,  the  vessel  is  placed  in  such  a 
situation  that  the  heat  may  be  kept  up  at  about  150°  F.,  and 
allowed  to  stand,  stirring  occasionally,  for  forty-eight  hours. 
These  precautions  being  attended  to,  we  have  uniformly  found 
that  any  failure  occurring  was  clearly  traceable  to  the  impurity 
of  the  indigo  or  weakness  of  the  acid  used." 

The  processes  for  producing  and  separating  the  two  acids  de- 
rived from  the  combination  of  sulphur  and  indigo  are  minutely 
given  by  Berzelius,  in  vol.  i.  of  his  w  Traits  de  Chemie,"  who 
states  this  curious  fact  illustrative  of  the  peculiar  affinities  of  wool 
with  certain  dyeing  substances.  Wool  or  flannel  thoroughly 
scoured,  when  immersed  in  the  blue  solution  of  indigo  with  sul- 


NOTES  UPON  INDIGO.  57 

phuric  acid,  acts  as  a  base  :  it  combines  gradually  with  the  acid 
blue,  and  becomes  itself  colored  of  a  deep  blue.  When  saturated 
with  color,  it  is  withdrawn.  Fresh  wool  is  introduced  until  the 
bath  yields  no  more  color.  If  sublimed  or  perfectly  pure  indigo 
is  used,  there  remains  in  the  bath  nothing  but  free  sulphuric  acid. 
The  wool  thus  plays  the  part  of  a  base  with  which  the  blue  acids 
combine.  The  dyed  wool  is  afterwards  washed  and  treated  in 
feeble  alkaline  bath  (ammonia),  which  redissolves  the  blue. 
This  method  of  purifying  the  Saxon  blue  is  still  practised  by 
French  manufacturers. 

The  combination  of  indigo  with  sulphuric  acid,  sometimes 
improperly  called  sulphate  of  indigo,  is  known  by  the  dyers 
here  and  in  England  under  the  name  of  chemic.  The  name  of 
chemic  blue  or  green  is  also  given  the  dyes  formed  from  the 
indigo  extract  hereafter  spoken  of.  It  is  largely  used  for  mak- 
ing certain  greens  required  in  Scotch  plaids. 

The  old  Saxon  blue  or  simple  solution  of  indigo  with  sulphuric 
acid  is  now  seldom  prepared  by  the  manufacturers  themselves. 
It  is  now  generally  prepared  for  them,  and  furnished  commercially 
under  the  name  of  indigo  extract.  The  finer  qualities  used  for 
fine  dyeing  and  printing  are  known  under  the  name  of  carmines 
of  indigo,  neutral  extract,  soluble  indigo,  ceruline,  &c. 

The  production  of  indigo  carmines,  which  are  simply  alkaline 
sulphindigotates  or  sulpho-purpurates,  is  founded  upon  their 
insolubility  in  a  liquid  charged  with  a  salt. 

If,  for  example,  we  dissolve  one  part  of  indigo  in  four  parts  of 
fuming  acid,  and  dilute  the  liquid  with  sixty  or  eighty  times  its 
weight  of  water,  it  will  contain,  besides  the  sulphindigotic  acid, 
an  excess  of  sulphuric  acid.  By  adding  one  part  of  crystals  of  soda 
so  as  to  neutralize  the  bath,  there  will  be  formed  not  only  sulph- 
indigotate  of  soda,  but  sulphate  of  soda  :  as  the  former  is  insolu- 
ble in  the  saline  liquid,  the  presence  of  the  sulphate  of  soda  causes 
the  precipitation  of  the  sulphindigotate  in  deep  blue  floccules. 
These  are  collected  on  woollen  filters  and  washed  to  remove  the 
sulphate  of  soda  and  a  green  coloring  material,  probably  a  modi- 
fied chlorophyl,  which  the  paste  often  contains,  and  which  has 
the  singular  property  of  fixing  itself  on  silk,  but  not  on  wool. 

8 


58 


NOTES  UPON  INDIGO. 


The  carmines  are  divided  according  to  their  richness  in  indigo 
into  simple  carmine  (4.96  per  cent  of  indigo,  water  89,  saline 
materials  57),  double  carmine  (10.2  per  cent  indigo,  water  85, 
salts  4-8),  triple  carmine  (12.4  percent  indigo  water,  73.7,  salts 
13.9).  A  species  of  solid  carmine  known  as  Boiley  blue  or 
purple  is  in  high  repute  in  France. 

The  carmines  may  be  tested  by  dyeing  a  specimen  of  wool  in 
an  acidulated  bath  to  which  cream  of  tartar  has  been  added. 
The  presence  of  the  green  matter,  so  objectionable  to  silk-dyers 
who  make  much  use  of  these  carmines,  is  detected  by  rubbing  a 
small  quantity  of  the  carmine  on  a  piece  of  glazed  paper,  which, 
when  the  color  dries,  gives  a  color  varying  from  blue  to  a  rich 
copper  color  :  if  any  green  coloring  matter  is  left,  it  shows  itself 
by  a  green  aureola  around  the  blue  color.  The  method  of 
applying  the  carmines  in*  dyeing  wool  and  silk,  —  for  they  are 
not  adapted  to  cotton  fabrics,  — as  given  by  M.  de  Kseppelin,  is 
as  follows  :  — 

The  operation  is  conducted  in  small  wooden  vats,  provided 
with  openings  for  manipulation,  and  pipes  for  inducting  steam 
to  heat  the  baths  to  the  proper  temperature.  It  consists  of  two 
parts,  that  of  mordanting  and  dyeing.  The  former  is  thus  con- 
ducted. 

For  each  kilogram  of  tissue  which  has  been  previously  scoured 
and  bleached,  there  are  provided  200  grammes  of  cream  of  tar- 
tar and  250  grammes  of  alum.  These  are  dissolved  in  the 
bath  of  wrater  of  the  vat,  the  temperature  is  raised  to  boiling 
heat,  and  the  tissue  is  immersed  in  the  bath  f  of  an  hour  while 
it  is  worked  over  through  the  opening  for  manipulation.  The 
pieces  are  then  taken  from  the  bath,  to  which  is  added  a  solu- 
tion of  the  carmine  in  water  containing  a  quantity  of  coloring 
matter  proportionate  to  the  intensity  of  the  blue  sought  for. 
The  solution  ought  to  be  prepared  with  care  and  passed  through 
a  silk  sieve,  so  that  the  small  insoluble  grains  which  might  have 
been  left  through  bad  fabrication  may  be  left  on  the  sieve. 
After  the  pieces  have  been  manipulated  in  the  colored  bath,  so 
as  to  exhaust  the  color  and  obtain  the  required  blue,  they  should 
be  rapidly  washed  in  running  water  and  dryed  in  the  shade. 


NOTES  UPON  INDIGO. 


59 


Silk  stuffs  are  dyed  in  the  same  way  ;  but  the  alum  should  be 
previously  applied  cold  by  means  of  a  saturated  solution  of 
alum,  in  which  the  stuffs  should  be  immersed  for  an  hour. 

COLORS  NOT  FAST. 

In  regard  to  all  the  combinations  of  indigo  with  sulphuric  •» 
acid,  including  the  carmines,  it  must  be  observed  that  their 
application  does  not  constitute  true  indigo  dyeing  :  the  colors  are 
not  fast.  It  is  not  pure  indigotine  which  is  fastened  on  the  tis- 
sues as  in  the  vat  dyeing,  but  another  compound  of  indigo  with 
the  sulphur.  Berzelius  observes  that  "the  color  of  soluble 
indigo  is  fully  as  alterable  and  fugacious  as  that  of  the  colors 
extracted  by  the  decoction  of  vegetable  materials.  By  a  long 
exposure  to  the  sun  the  indigo  blue  is  destroyed  :  it  becomes 
green  during  evaporation,  and  changes  its  nature."  The  car- 
mines as  well  as  the  sulphur  acids  are  easily  decolorized  by 
reducing  agents,  such  as  hydrogen  and  sulphuretted  hydrogen, 
although  they  gradually  assume  their  original  color  when  ex- 
posed to  the  atmosphere.  We  are  informed  by  some  of  the 
older  dealers  that  imported  cloths  and  merino  stuffs  known  as 
"Saxony"  were  formerly  largely  sold  in  our  shops,  but  that, 
notwithstanding  their  attractiveness  to  purchasers,  they  were 
objectionable  on  account  of  the  instability  of  their  color. 

APPLICATION  OF  INDIGO  IN  PRINTING  STUFFS. 

Our  notes  would  be  incomplete  without  some  reference  to  the 
uses  of  indigo  in  printing  fabrics.  In  pursuing  this  branch,  we 
are  embarrassed  on  the  one  hand  by  the  consideration  that  the 
subject  is  too  technical  for  the  general  reader,  and  on  the  other 
by  the  consciousness  that  it  would  be  presumption  in  us  to  attempt 
to  instruct  those  skilled  in  the  art.  It  may  not,  however,  be 
without  benefit  in  producing  a  higher  appreciation  of  science  for 
the  general  reader  to  observe  how  science  comes  in  play,  even  in 
the  printing  of  a  single  color ;  while  to  the  skilled  reader  our 
notes  may  possibly  be  of  value  as  a  vehicle  for  conveying  some 
receipts  taken  from  works  not  easily  accessible. 


60 


NOTES  UPON  INDIGO. 


PRINTING  STUFFS  OF  WOOL  AND    SILK,  AND  STUFFS  WITH 
COTTON  WARPS. 

This  branch  of  our  subject  is  directly  allied  to  the  one  last 
considered,  the  application  of  the  compounds  of  sulphur  and 
indigo ;  for  indigo  is  applied  to  printing  wool  and  silk  princi- 
pally in  the  form  of  indigo  carmines.  These  applications  are  less 
numerous  than  they  were  formerly,  since  they  have  been  replaced 
by  Prussian  blue,  and  more  recently  by  the  aniline  blues,  which 
are  now  generally  used.  When  the  carmines  are  used,  it  is  for 
making  sky  blues,  and  they  enter  into  the  composition  of  some 
greens  and  browns.  The  salts  of  alumina  and  vegetable  acids 
are  used  to  fix  the  indigo  carmine  upon  tissues  of  wool  and  silk. 
Some  receipts  recommended  by  M.  de  Kseppelin,  himself  a 
practical  printer,  are  given  in  a  note.* 

*  BLUE  NO.  1. 

Indigo  carmine   400  grammes. 

Alum   100  „ 

Oxalic  acid   150  „ 

Boiling  water  \\  litre 

Gum  water  prepared  in  proportion  of  1  kilo- 
gram to  the  litre  1|  litre 

GREEN  NO.  1. 

Gum  water  as  above   12  litres. 

Cuba  lac   12  „ 

Alum   1  kilogram,   500  grammes. 

Oxalic  acid   2  „ 

Indigo  carmine   4  „ 

BOUILLON  FOR  THE  GREENS  AND  BLUES. 

Boiling  water  12  litres. 

Alum   600  grammes. 

Oxalic  acid   750  „ 

Gum  water  12  „ 

SKY  BLUE  FOR  WOOLLEN  STUFF  WITH  COTTON  WARP. 

First  solution.  — Boiling  water  4  litres. 

Cyanuret  of  iron  and  potash  .  800  grammes. 

Second  solution.  —  Boiling  water  2  „ 

Tartaric  acid   300  „ 

Third  solution.  —  Cold  water  3  „ 

Sulphuric  acid   300 

Pour  in  the  first  solution,  then  the  second  and  third,  agitating  the  color  with  a 
spatula  after  each  new  addition. 

The  following  mixture  is  afterwards  applied  to  the  stuff :  — 

Gum  water  12  litres. 

Water   .•  6  „ 

Blue  No.  1  for  wool  3  „ 


NOTES  UPON  INDIGO. 


In  printing  tissues  of  wool  with  cotton  warp,  the  carmines 
are  not  used  alone.  They  are  combined  in  certain  proportions 
with  cyanites  of  iron  and  potash,  to  obtain  upon  the  cotton  a 
blue  color  of  equal  intensity  with  that  produced  by  the  carmines 
upon  wool.  It  is  also  necessary  to  previously  mordant  the 
fabrics  by  means  of  a  solution  of  oxide  of  tin  or  caustic  soda,^ 
which  is  precipitated  on  the  fibres  by  passing  through  a  bath  oft 
water,  to  which  sulphuric  acid  has  been  added.  \ 

APPLICATIONS  OF  INDIGO  IN  PRINTING  COTTON  FABRICS. 

Before  entering  upon  methods  used  in  large  establishments, 
it  may  not  be  without  interest  to  observe  the  processes  still  used 
in  Java  for  printing  calicoes,  which  the  natives  prefer  to  any 
imported  from  Europe.  In  Java  there  are  no  factories,  and  the 
women  in  each  family  make  and  dye  or  print  all  the  cotton 
cloths  required  for  their  own  consumption.  They  apply  by 
means  of  a  brush  or  pencil,  which  they  use  with  great  skill,  to 
the  cotton  tissue  which  they  wish  to  cover  a  thin  coating  of 
wax  mixed  with  a  little  resin,  the  wax  being  applied  to  all  the 
parts  where  the  design,  which  has  been  first  traced  upon  the 
cloth,  requires  that  the  fabric  should  remain  uncolored.  They 
then  immerse  the  stuff  several  times  in  an  indigo  vat  until  they 
have  obtained  the  desired  tint.  The  stuff  is  afterwards  washed  and 
dried  for  a  new  application  of  the  wax,  carefully  applied  with  a 
pencil  as  before.  The  cloth  is  then  immersed  in  a  bath  of  a  differ- 
ent color,  made  with  madder  or  catechu,  but  always  of  some  dye 
which  is  perfectly  stable ;  and  the  operation  is  repeated  accord- 
ing to  the  number  of  colors  desired.  By  these  successive  appli- 
cations of  wax  and  immersions  into  different  vats,  they  succeed 
in  producing  very  complicated  and  harmonious  colors,  while  no 
European  goods  compare  with  them  in  stability  of  dye. 

In  the  European  and  our  own  manufacture,  the  blue  bot- 
toms upon  vegetable  fibres,  made  by  immersion  in  the  indigo 
vat,  are  combined  with  white  impressions,  or  others  variously 
colored,  by  two  distinct  methods.  Sometimes  there  is  printed 
upon  the  cloth  before  dyeing  in  the  indigo  vat  a  preparation  called 
a  reserve  or  resist,  which  prevents  the  indigotine  from  being 
deposited  in  the  places  where  it  is  applied.     Sometimes,  on  the 


62 


NOTES  UPON  INDIGO. 


contrary,  the  indigo,  which  has  been  uniformly  fixed  upon  the 
fabric,  is  destroyed  in  certain  places  marked  out  by  printing 
upon  them  certain  chemical  agents,  called  discharges. 

The  reserves  are  mechanical,  resisting  the  penetration  of  the 
dye,  such  as  wax  and  pipe  clay,  or  chemical.  The  last,  through 
these  acid  or  oxidizing  properties,  cause  the  precipitation  of  the 
indigotine  before  it  has  touched  the  fibre  or  penetrated  into  its 
pores.  Such  are  the  salts  of  copper  and  bi-chlorate  of  mercury. 
Other  bodies  perform  the  part  both  of  mechanical  and  chemical 
reserves.  The  salts  of  zinc  or  alumina,  for  instance,  which  are 
frequently  used,  produce  at  the  same  time  a  deposit  of  indigo 
white  and  a  gelatinous  covering  of  hydrated  oxide  of  zinc  or 
aluminium.  The  composition  of  a  good  reserve  is  declared  to 
be  principally  a  question  of  good  proportions  of  the  constituent 
parts,  varying  with  the  strength  of  the  vat  and  the  intensity  of 
the  blue  which  is  desired  to  be  reserved.  The  first  condition  is 
that  it  hardens  immediately  after  immersion  in  the  vat :  if  it 
softens,  on  the  contrary,  it  will  cause  the  running  of  the  color. 
In  other  words,  the  acidity  of  the  impression  should  be  propor- 
tionate to  the  strength  and  alkaline  character  of  the  vat.  The 
white  reserve,  that  most  generally  used,  is  composed  of  pipe  clay, 
gum,  verdigris,  and  sulphate  of  copper.  The  styles  of  work 
produced  by  dipping  with  reserves  are  generally  of  a  cheap  and 
low  class.  The  system  is  clumsy  and  expensive,  and  is  only 
tolerated  because  of  the  want  of  a  method  of  directly  applying 
indigo,  which  will  yield  the  deepest  shades. 

Certain  styles,  formerly  in  great  vogue,  called  Lapis,  and 
forming  one  of  the  richest  branches  of  the  cotton-printing  indus- 
try, are  founded  upon  the  use  of  reserves  ;  and  in  these  styles,  by 
very  simple  means  which  we  shall  not  attempt  to  describe,  differ- 
ent colors  produced  from  madder,  catechu,  &c,  are  produced 
upon  the  fabric  so  perfectly  surrounded  by  blue  that  the.  eye 
cannot  detect  the  slightest  want  of  continuity.  This  fabrication 
has  the  greatest  perfection  in  Russia.  The  imitation  cashmere 
fabrics  of  cotton  imported  from  that  country,  formerly  much  in 
fashion  for  dressing-gowns,  are  specimens  of  this  fabrication. 
The  great  stability  of  the  colors  is  a  remarkable  feature  of  these 
goods. 


NOTES  UPON  INDIGO. 


63 


The  system  of  resists  or  reserves  possesses  the  inconveniences 
of  not  producing  impressions  of  great  firmness,  and  of  requiring 
very  strong  vats.  When  the  strength  of  the  vat  is  partially 
exhausted,  they  may  be  thrown  aside.  These  inconveniences 
are  obviated  by  the  system  of  discharges  (enlevages).  In 
this  system  the  cloths  are  vat  dyed  of  a  uniform  blue.  The 
strength  of  the  vat  is  of  less  importance,  and  it  can  be  used 
until  the  indigo  is  quite  exhausted.  The  means  of  destroying 
the  indigo  which  has  been  fixed  upon  the  fibre  are  founded  on 
the  use  of  active  oxidizing  agents,  which  transform  the  insoluble 
indigotine  into  soluble  isatine.  The  agent  generally  used  is 
chromic  acid.  As  this  acid  cannot  be  incorporated  with  the 
thickening  to  be  printed,  as  the  thickening  would  produce  oxide 
of  chrome,  the  cloth  is  passed  through  a  strong  solution  of 
chromate  of  potash,  and  dried  in  the  shade.  The  required  pat- 
tern is  then  printed  on  the  cloth  with  a  mixture  whose  principal 
elements  are  acids  which  are  susceptible  of  setting  free  the 
chromic  acid  on  the  tissue,  which  then  acts  upon  the  indigo 
producing  a  white  pattern.  The  acid  generally  employed  for 
freeing  the  chromic  acid  is  oxalic  acid,  thickened  with  British 
gum,  dextrine,  or  starch,  with  the  addition  of  pipe  clay.  To 
prevent  running,  nitric,  sulphuric,  or  tartaric  acid  are  some- 
times used.* 

*  Schutzenberger  gives  the  following  receipts  :  — 

PREPARATION  FOR  DISCHARGE. 

Water  2  litres. 

Yellow  chromate  ..    .    500  grammes. 

WHITE  DISCHARGE  ON  BLUE  BOTTOM. 

Tartaric  acid   3  kilograms. 

Oxalic  acid   250  grammes. 

Burnt  starch   4  kilograms. 

Nitric  acid   500  grammes. 

Water   4  litres. 

De  Kseppelin  gives  the  following:  — 

WHITE  DISCHARGE  ON  BLUE. 

Water   2  litres. 

Starch   1  kilogram,  800  grammes. 

Oxalic  acid   500  grammes. 

Tartaric  acid  '  .    .    .    .  250  grammes. 

Sulphuric  acid     .    375  grammes. 

The  pieces,  having  been  dyed  blue,  are  then  placed  in  a  solution  of  bichromate  of 
potash  in  water,  which  is  prepared  in  the  ratio  of  50  to  60  grammes  to  the  litre,  according 


64 


NOTES  UPON  INDIGO. 


By  the  method  of  discharges  the  white  designs  upon  blue  are 
brought  out  with  a  distinctness  which  it  is  impossible  to  obtain 
by  resists,  while  the  most  delicate  work  of  the  graver  can  be 
exactly  reproduced  upon  the  tissue. 

APPLICATION  OF  INDIGOTINE  BY  PRINTING. 

The  first  step  in  the  art  of  printing  indigo  tine  upon  calicoes 
was  the  application  of  what  is  called  pencil  blue.  Instead  of 
immersing  the  fabrics  in  an  indigo  vat,  the  indigo  white  formed 
in  a  very  strong  indigo  vat  was  thickened  and  applied  locally  to 
certain  places  on  the  cloth.  The  preparation  was  painted  upon 
the  cloth  by  means  of  pencils  made  of  willow  sticks,  the  ends  of 
which  were  broomed  up  into  a  kind  of  brush.  The  style  was 
hence  called  pencil  blue.  The  methods  now  used  to  apply  white 
indigo  locally  are  of  two  kinds.  The  china  blue  process,  and  the 
solid  blue  process,  sometimes  called  fast  or  precipitated  blue. 
The  china  blue  process  derives  its  name  from  the  resemblance 
of  its  color  to  the  blue  on  the  old  china  ware.  It  has  great 
depth  of  tint,  and  permanency.  It  is  scarcely  used  now,  except 
for  certain  articles  requiring  great  depth  of  color,  such  as  cer- 
tain furniture  goods,  and  by  the  Germans  and  Swiss  for  the 
manufacture  of  calicoes  for  exportation  to  India. 

We  do  not  venture  to  condense  the  descriptions  at  our  hand 
of  the  processes  for  applying  the  china  blue  and  the  solid  blue, 
and  translate  those  furnished  by  chemists  of  high  authority. 
After  the  method  indicated  by  Darwin  in  his  recent  works,  we 
present  them  in  smaller  type,  with  the  perhaps  unnecessary 
suggestion  that  they  may  be  passed  over  by  the  general  reader. 

China  blue.  —  The  theory  of  this  printing  blue,  says  Schutzenber- 
ger,  is  very  simple.  The  indigo,  reduced  to  an  impalpable  powder  and 

to  the  intensity  of  the  blue.  The  pieces  thus  prepared  must  be  dried  away  from  direct 
solar  light  or  too  much  heat.  In  fact,  under  the  action  of  these  agents,  the  bichromate 
would  be  decomposed  and  the  tissue  altered.  The  pieces  are  often  rolled  up  to  prevent 
this  effect.  After  the  pieces  are  printed,  they  are  passed  into  a  vessel  containing  water 
and  holding  chalk  in  suspension  in  sufficient  quantity  to  give  it  a  milky  aspect.  The 
temperature  of  the  bath  is  raised  to  60°  R.  The  excess  of  acid  of  the  color  applied  is 
saturated  by  the  chalk,  and  the  excess  of  bichromate  of  potash  with  which  the  tissue  is 
impregnated  is  dissolved  in  the  bath.  The  pieces  are  afterwards  washed  and  passed 
through  slightly  soapy  water. 


NOTES  UPON  INDIGO. 


65 


thickened,  is  printed  by  a  plate  or  roller.  After  drying,  the  tissue 
seems  dyed  blue,  more  or  less  deep,  according  to  the  proportion  of 
coloring  material  used  ;  but  it  is  only  a  blue  of  application,  which  can 
be  removed  with  the  thickening,  by  the  slightest  washing.  The  object 
is  now  to  reduce  and  redissolve  the  indigotine  in  place  to  enable  it  to 
penetrate  the  fibre  at  the  end  of  a  consecutive  oxidization,  and  with- 
out producing  a  running  of  the  color  or  altering  the  purity  and  dis- 
tinctness of  the  contours  of  the  design.  I  owe  to  M.  Ed.  Schwartz 
some  valuable  hints  upon  the  fabrication  of  this  style,  which  is  also 
described  with  much  care  and  details  in  the  treatise  on  printing  by 
M.  Persoz. 

The  reduction  of  the  indigo  is  obtained  by  alternate  passages  of  the 
printed  tissue  into  vats  containing,  — the  first,  quicklime  slacked  ;  the 
second,  sulphate  of  iron  ;  the  third,  soda.  The  operation  is  termi- 
nated by  a  passage  through  a  bath  of  sulphuric  acid,  which  removes 
the  oxide  of  iron  and  precipitates  the  indigo  white  by  hastening  its 
oxidation. 

The  success  depends  upon  the  composition  of  the  color  printed,  and 
above  all  upon  the  strength  of  the  vats  of  immersion  and  the  duration 
of  the  treatment. 

The  operator  uses  six  vats,  —  for  instance,  two  lime  vats,  provided 
each  with  12  kilograms  of  lime;  a  copperas  vat  at  70  Beau  me  ;  a 
caustic  soda  vat  marking  140  Beaume  ;  a  sulphuric  acid  vat  with 
500  grammes  of  acid  (par  mesure  d'eau)  ;  and  finally  a  vat  of  pure 
water. 

The  receipts  for  printing  are  :  — 

1.    THE  BLUE  PREPARATION. 

Ground  indigo  4  kilograms. 

Acetate  of  iron  10  litres. 

Sulphate  of  iron  1  kilogram. 

Water  10  litres. 

Gum  Senegal  6  kilograms. 

Pass  through  a  sieve  ;  leave  some  time  at  rest,  and  stir  whenever 
used.  Caraccas  indigo  is  preferred  because  it  can  be  broken  into 
a  finer  powder  and  gives  a  finer  paste. 

2.    COLORS  POR  ROLLER  PRINTING  NOS.  1,  2,  3,  4. 

The  blue  preparation  above  1,  1,  3,  4. 

Acetate  of  iron  containing  700  grammes  of  gum  per  litre    2,  1J,  J. 

Gum  water  at  600  grammes  per  litre  16,  2 J,  i,  \. 

These  proportions  can  be  varied  according  to  the  tint  desired. 

9 


66 


NOTES  UPON  INDIGO. 


The  piece  is  treated  a  quarter  of  an  hour  in  the  first  lime  vat  by 
giving  it  a  light  movement  from  above  to  below  ;  it  is  left  a  quarter  of 
an  hour  in  repose  in  the  sulphate  of  lime  vat ;  a  quarter  of  an  hour 
in  the  second  lime  vat  ;  a  quarter  of  an  hour  in  the  copperas  vat  ; 
five  minutes  in  the  caustic  soda  ;  half  au  hour  in  the  sulphuric  acid, 
and  then  thoroughly  rinsed. 

To  each  lime  vat  there  is  given  2  kilograms  of  lime  per  piece  of 
cloth.  To  the  vitriol  vat  there  is  added  50  kilograms  of  sulphate  of 
iron  for  each  dozen  pieces.  The  soda  vat  is  renewed  after  5  pieces 
by  the  addition  of  12  kilograms  of  salt  of  soda,  which  has  first  been 
made  caustic.  The  acid  vat  receives  25  kilograms  of  acid  after  5 
pieces,  and  ought  to  be  renewed  whenever  it  becomes  saline.  The 
other  vats  must  be  cleared  out  whenever  the  deposit  becomes  too 
great  for  success. 

M.  Ed.  Schwartz  recommends  as  important  conditions,  (1)  the 
perfect  causticity  of  the  tissue,  and  an  average  strength  of  140  Beaume ; 
(2)  the  neutrality  of  the  sulphate  of  lime  vat.  For  this  end  old  iron 
should  be  boiled  in  it. 

After  leaving  the  sulphuric  acid  vat  the  pieces  are  rinsed  in  the 
water  vat,  then  in  river  water,  and  afterwards  should  be  soaked  in  a 
sulphuric  acid  bath  at  40  Beaume,  for  the  purpose  of  dissolving  the 
last  traces  of  the  peroxide  of  iron  adhering  to  the  fibre.  The  fabric 
is  then  washed  in  water  and  finally  passed  through  a  soapy  water  at 
40°  R. 

Solid  or  precipitated  blue,  Schiitzenberger's  receipt.  —  The  process 
consists  in  printing  indigo  white  precipitated  in  a  vat,  in  a  thick  paste 
to  dissolve  it  on  the  tissue  by  a  passage  through  an  alkaline  bath 
(lime  or  soda),  and  of  reprecipitating  it  by  oxidizing  it  as  soon  as  it 
has  entered  the  fibre. 

It  is  then  the  china  blue  process,  minus  the  reduction  which  is 
made  before  printing,  and  consequently  minus  the  sulphate  of  iron 
vat. 

Indigo  white  is  too  alterable  to  be  printed  with  success,  so  it  is 
generally  precipitated  in  combination  with  a  stannic  hydrate  (hydrate 
of  a  salt  of  tin),  which  gives  it  body  and  preserves  it  from  a  too 
rapid  oxidation. 

The  stannic  indigotate  in  paste,  or  as  it  is  generally  called  precipi- 
tate of  indigo,  is  prepared  by  turning  into  the  clear  portion  of  a 
strong  copperas  vat  an  acid  solution  of  protochlorate  of -tin,  and  filter- 
ing it  upon  woollen  filters,  —  as  much  as  possible  away  from  the  air. 


NOTES  UPON  INDIGO. 


67 


It  would  be  better  to  prepare  a  strong  tin  vat  by  heating  a  mixture 
of  indigo,  caustic  soda,  and  protochlorate  of  tin,  and  to  precipitate  by 
chlorohydric  acid.* 

The  deposit  is  made  into  a  paste  with  gum  water  ;  a  salt  of  tin 
is  often  added  to  prevent  oxidatiou.  It  is  important  to  prevent  the 
transformation  of  the  indigo  white  into  indigotine  before  printing. 
This  indigotine  would  not  fix  itself  on  the  fabric.  Moreover,  after 
printing,  it  is  necessary  to  hasten  the  dissolution  of  the  indigo  white 
to  enable  it  to  penetrate  the  fibre.  It  is  sufficient  for  this  end  to  pass 
it  through  milk  of  lime.  The  stannic  combination  is  immediately  de- 
stroyed ;  the  colorable  matter  unites  itself  with  the  lime,  and  the  color 
passes  into  a  pale  gray  with  apple  green.  The  indigo  white  becomes 
momentarily  soluble  ;  but  the  presence  of  the  excess  of  lime  and  the 
thickening,  as  well  as  the  attractive  affinity  of  the  thickening,  prevent 
any  running. 

The  piece  on  issuing  from  the  lime  water  is  placed  in  running 
water,  when  reoxidation  commences,  which  this  time  fixes  the  color. 
The  piece  is  finally  passed  through  a  sulphuric  acid  bath  to  absorb 
the  lime,  and  washed. 

By  adding  to  the  color  a  salt  whose  base  precipitates  in  the  milk 
of  lime  and  oxidizes  in  the  running  water,  and  replacing  the  simple 
acid  bath  by  an  acid  bath  with  yellow  prussite,  the  intensity  of  the 
blue  is  increased  through  the  formation  of  Prussian  blue. 


*  Mr.  T.  P.  Shepard  gives  in  his  valuable  "  Receipts  for  Calico  Printing,"  published 
in  1872,  the  following:  — 

NO.  52.     INDIGO  PRECIPITATE  FOR  FAST  BLUE  AKT)  GREEN. 

10  pounds  quicklime,  slacked  with 
6£  gallons  water;  then 

2  pounds  ground  indigo  finely  rubbed  in  water  are  stirred  in ;  then  add 
6  pounds  copperas  dissolved  in  5  gallons  of  water;  then  add 
5  gallons  hot  water  and 
15  gallons  cold  water. 

Stir  well  from  time  to  time,  until  the  liquid  has  assumed  a  yellow  color 
and  deep  blue  veins  or  streaks  appear  on  its  surface.  When  this  moment 
arrives,  draw  off  the  clear  liquor,  and  precipitate  every  ten  quarts  of  it 
with 

£  pound  tin  crystals,  dissolved  in  £  pound  muriatic  acid. 

To  the  remainder  of  the  mixture  of  lime  and  indigo,  15  gallons  of  water 
may  be  added,  and  the  whole  stirred ;  and  when  settled,  the  indigo  may 
be  precipitated  from  the  clear  liquor  as  before.  This  operation  may  be 
repeated  a  second  time  before  all  the  indigo  is  exhausted. 

The  indigo  precipitate  is  to  be  collected  on  a  muslin  filter,  and  well  squeezed  out. 


68  NOTES  UPON  INDIGO. 

Although  we  have  seen  beautiful  effects  from  the  application 
of  the  solid  blue  of  indigo  on,  prints  at  our  Pacific  Mills,  the 
colors  produced  by  Prussian  blue  and  aniline  are  so  much  more 
brilliant  and  easy  of  application  that  the  use  of  indigo  in  print- 
ing goods  for  ordinary  consumption  is  likely  to  decline  rather 
than  increase.  It  will  be  otherwise  if  we  should  ever  manufac- 
ture for  the  East  India  markets.  Here  is  a  field  still  open  for 
our  manufacturers.  Mr.  Watson,  in  his  beautiful  work  on 
"  The  Costumes  of  the  People  of  India,"  remarks  that  "British 
manufacturers  have  hitherto  failed  to  appreciate  Oriental  tastes 
and  habits,  and  hence  supply  but  an  insignificant  part  of  the 
clothing  of  the  two  hundred  million  persons  that  form  the  pop- 
ulation of  what  is  commonly  spoken  of  as  India."  The  great 
defect,  he  observes,  is  the  want  of  stability  of  color  in  the 
cotton  fabrics  introduced, — this  stability  being  an  imperative 
demand  in  the  Oriental  markets. 

The  applications  of  indigo  to  cotton  fabric  are  altogether 
secondary,  in  our  mind,  to  its  relations  to  the  woollen  manufac- 
ture. If  we  have  felt  called  upon  to  say  a  word  in  behalf  of 
the  most  ancient  and  best  ally  which  the  fibre  of  wool  has  ever  had, 
it  is  because  the  vividness  of  color  of  the  new  products  of  coal, 
and  the  fascination  which  the  application  of  the  recent  discoveries 
of  science  always  possesses,  is  threatening  the  eclipse  of  the 
more  ancient  sober  and  solid  dyes.  Let  the  new  colors  have 
their  place  as  auxiliaries,  not  as  substitutes  for  the  ancient 
dyes.  Let  them  serve  to  give  a  bloom*  to  goods,  but  let  the 
foundation  be  the  good  old  dyes  which  the  experience  of  ages  has 
proved  to  be  the  most  unalterable  by  light  and  air.  The  recent 
wonderful  discovery  of  alizarine,  or  artificial  madder,  in  coal 
tar  products,  has  led  practical  men  to  expect  too  much  from  sci- 
ence. The  opinion  is  quite  prevalent  among  manufacturers 
that  artificial  indigotine  has  already  been  obtained  from  the 

*  Guernsey  Blue.  —  The  darkest  of  the  Nicholson  Fast  Blues.  On  a  bottom  of  bark- 
wood,  camwood,  madder,  or  inferior  indigo,  produces  an  indigo  blue  which  will  stand  all 
the  acid  tests  the  same  as  colors  made  from  indigo. 

Serge  Blue.  —  It  will  be  found  very  serviceable  to  give  bloom  to  goods  dyed  with 
indigo,  and  by  itself  shows  a  very  grood  indig  >  tost  with  nitric  acid.  —  Instructions  for 
Working  the  Atlas  Works  Aniline  Dues. 


i 


NOTES  UPON  INDIGO. 


69 


same  source.  And  some  manufacturers  are  sanguine  that  the 
difficulties  of  indigo-dyeing  will  thus  be  resolved.  It  is  not 
improbable  —  for  what  is  impossible  to  modern  chemistry  ? — 
that  this  result  will  yet  be  partially  obtained.  But  we  have 
looked  over  all  the  recent  foreign  chemical  reviews,  and  person- 
ally consulted  some  of  our  best  chemists,  and  we  can  find  no 
authority  for  the  prevailing  opinion  that  artificial  indigotine 
has  been  produced.  If  the  production  of  artificial  indigotine 
should  be  realized,  the  only  benefit  would  be  the  possible  cheap- 
ening of  the  material.  The  difficulties  of  the  indigo  vat  would 
still  remain  ;  for  we  cannot  too  often  repeat,  that  in  the  very 
difficulties  of  the  process,  or  in  the  insolubility  of  blue  indigo- 
tine by  ordinary  agents,  consists  the  excellence  of  the  dye. 


APPENDIX. 
DYEING  WOOL  IN  THE  WARM  INDIGO  VAT. 

[Extract  from  Dumas's  Lectures  on  Dyeing.] 

The  value  attached  by  practical  wool-dyers  to  the  following  induces 
us  to  publish  it  without  condensation  :  — 

Indigo  Blue.  —  We  give  a  solid  dye  of  indigo  blue  to  wool  by  plunging  it 
into  an  alkaline  solution  of  indigo  white,  and  then  exposing  it  to  contact  with 
the  air.  The  solution  of  indigo  white  is  prepared  in  a  vessel  usually  from  eight 
to  nine  feet  in  depth,  and  six  to  seven  feet  in  diameter.  This  size  is  very  con- 
venient for  the  requisite  manipulations,  and  presents  a  large  volume  of  water, 
which,  when  once  heated,  is  capable  of  preserving  a  high  temperature  for  a  long 
time.  This  vessel  should  be  made  of  wood  or  copper.  It  always  bears  the  name 
of  vat.  These  vats  are  covered  with  a  wooden  lid,  divided  into  two  or  three 
equal  segments.  Over  this  lid  are  spread  some  thick  blankets.  Without  this 
precaution  the  bath  would  come  in  contact  with  the  atmospheric  air,  a  portion 
of  the  indigo  would  absorb  oxygen  and  become  precipitated.  There  would  also 
be  a  great  waste  of  heat. 

A  most  necessary  operation,  and  one  which  has  to  be  frequently  repeated, 
consists  in  stirring  up  the  deposit  of  vegetable  and  coloring  matter  which  is 
formed  in  the  vat,  and  intimately  mixing  it  in  the  bath.  Eor  this  purpose  we 
employ  a  utensil  called  a  rake,  which  is  formed  of  a  strong  square  piece  of  wood, 
set  on  a  long  handle.  The  workman  takes  hold  of  this  with  both  hands,  and, 
dipping  the  flat  surface  into  the  deposit  at  the  bottom  of  the  vessel,  he  quickly 


70 


NOTES  UPON  INDIGO. 


draws  it  up  until  it  nearly  reaches  the  surface,  when,  giving  it  a  gentle  shake,  he 
discharges  the  matter  again  through  the  liquor  of  the  bath.  This  manoeuvre  is 
repeated  until  the  whole  of  the  deposit  seems  to  be  removed  from  the  bottom  of 
the  vessel.  Before  the  tissue  is  dipped  into  the  dye-bath,  it  should  be  soaked  in 
a  copper  full  of  tepid  water ;  it  is  then  to  be  hung  up  and  beaten  with  sticks.  In 
this  state  it  is  plunged  into  the  vat ;  it  thus  introduces  less  air  into  the  bath, 
while  it  is  more  uniformly  penetrated  by  the  indigo  solution.  The  cloth  is  now 
kept  at  a  depth  of  from  two  to  three  feet  below  the  surface  of  the  liquid,  by 
means  of  an  open  bag  or  piece  of  network  fixed  in  the  interior  of  an  iron  ring, 
which  is  suspended  by  cords,  and  fixed  to  the  outside  of  the  vat  by  means  of  two 
small  iron  hooks ;  the  bag  is  thus  drawn  backwards  and  forwards  without  per- 
mitting it  to  come  in  contact  with  the  air.  When  this  operation  has  been  con- 
tinued for  a  sufficient  length  of  time,  the  cloth  is  wrung  and  hung  up  to  dry. 

Flock  wool  is  also,  for  the  purpose  of  dyeing,  enclosed  in  a  fine  net,  which 
prevents  the  least  particle  from  escaping,  and  which  is  fixed  in  the  bath  in  the 
same  way  as  in  the  foregoing  case. 

The  many  inconveniences  attending  the  use  of  wooden  baths,  which  neces- 
sitate the  pouring  of  the  liquor  into  a  copper  for  the  purpose  of  giving  it  the 
necessary  degree  of  heat,  have  led  to  the  general  employment  of  copper  vessels. 
These  are  fixed  in  brickwork,  which  extends  half  way  up  their  surface,  whilst  a 
stove  is  so  constructed  at  this  elevation  that  the  flame  shall  play  around  their 
upper  part.  By  this  means  the  bath  is  heated  and  kept  at  a  favorable  tempera- 
ture without  the  liquor  being  obliged  to  be  removed. 

The  potash  vats  are  usually  formed  of  conical-shaped  coppers,  surrounded  by 
a  suitable  'furnace.  These  may  be  constructed  with  less  depth,  inasmuch  as 
there  is  less  precipitation  induced  in  the  liquor.  By  using  steam  for  heating  the 
vats,  we  might  dispense  with  the  employment  of  copper  vessels,  and  so  return  to 
those  of  wood. 

The  vats  employed  for  dyeing  wool  are  known  under  the  names  of  the  pastel 
vat,  the  woad  vat,  the  potash  vat  the  tartar-lee  vat,  and  the  German  vat. 

Pastel  Vat*— The  first  care  of  the  dyer  in  preparing  the  vat  should  be 
to  furnish  the  bath  with  matters  capable  of  combining  with  the  oxygen,  whether 
directly  or  indirectly,  and  of  giving  hydrogen  to  the  indigo.  We  must,  how- 
ever, be  careful  to  employ  those  substances  only  which  are  incapable  of  impart- 
ing to  the  bath  a  color  which  might  prove  injurious  to  the  indigo.  These 
advantages  are  found  in  the  pastel,  the  woad,  and  madder.  This  latter  sub- 
stance furnishes  a  violet  tint  when  brought  into  contact  with  an  alkali,  and  by 
the  addition  of  indigo  it  yields  a  still  deeper  shade. 

In  preparing  the  Indian  vat,  we  ordinarily  employ  one  pound  of  fine  madder 
to  two  pounds  of  indigo.  The  madder  is  here  especially  useful,  by  reason  of  the 
avidity  of  some  of  its  principles  for  oxygen. 

The  pastel  vat,  when  prepared  on  a  large  scale,  ordinarily  contains  from  18 
to  22  lbs.  of  indigo  ;  11  lbs.  of  madder  would  suffice  for  this  proportion,  but  we 
must  also  bear  in  mind  the  large  quantity  of  water  which  we  have  to  charge 
with  oxidizabie  matters.    I  have  invariably  seen  the  best  results  from  employ- 


*  The  distinction  between  pastel  and  woad  is  not  very  clear.  Schutzenberger 
says:  "  Pastel,  woad,  and  satis  tinctoria  is  a  plant  of  the  family  of  the  crucifera.  It 
would  seem,  however,  that  the  term  pastel  as  used  by  the  old  French  dyers  is  applied  to 
the  leaves  of  the  woad  which  have  been  fermented,  formed  into  paste,  and  afterwards 
into  balls,  and  which  contain  much  blue  coloring  matter.  And  the  term  woad  as  dis- 
tinguished from  pastel  \s  applied  to  the  unfermented  plant." 


NOTES  UPON  INDIGO.  1\f"" 

/  * 

ing  22  lbs.  to  a  vat  of  this  size.  Bran  is  apt  to  excite  the  lactic  fermentation  tM^ 
the  bath,  and  should  therefore  not  be  employed  in  too  large  a  quantity;  7  to'fc} 
lbs.  will  be  found  amply  sufficient.  .  y~\ 

Weld,  which  is  often  used,  is  rich  in  oxidizable  principles;  it  turns  sour,  and?" 
passes  into  the  putrid  fermentation  with  facility.    Some  dyers  use  it  very  freely  ;\  / , 


passes  into  tne  putria  Termeniauon  wiui  niumiy.     ooiue  uyers  use  il  very  nueiy  ;  V*  ^ 
but  ordinarily  we  employ  in  this  bath  an  equal  quantity  of  it  to  that  of  the  bran.  \  ' 
Sometimes  weld  is  not  added  at  all. 

In  most  dye-houses  the  pastel  is  pounded  before  introducing  it  into  the  vat. 
Some  practical  men,  however,  maintain  that  this  operation  is  injurious,  and  that 
it  interferes  with  its  durability.  This  is  an  opinion  which  deserves  attention. 
The  effect  of  the  pastel,  when  reduced  to  a  coarse  powder,  is  more  uniform  ;  but 
this  state  of  division  must  render  its  alterations  more  rapid.  When  the  bath  has 
undergone  the  necessary  ebullition,  the  pastel  should  be  introduced  into  the  vat, 
the  liquor  decanted,  and  at  the  same  time  7  or  8  lbs.  of  lime  added,  so  as  to 
form  an  alkaline  lye  which  shall  hold  the  indigo  in  solution.  Having  well 
stirred  the  vat,  it  should  be  set  aside  for  four  hours,  so  that  the  little  pellets  shall 
have  time  to  become  thoroughly  soaked,  both  inside  and  out,  and  thus  be  pre- 
pared for  fermentation.  Some  think  coverings  are  to  be  spread  over  the  vat, 
so  as  to  preserve  it  from  contact  with  the  atmosphere.  After  this  lapse  of  time, 
it  is  to  be  again  stirred.  The  bath  at  this  moment  presents  no  decided  character ; 
it  has  the  peculiar  odor  of  the  vegetables  which  it  holds  in  digestion  ;  its  color  is 
of  a  yellowish-brown. 

Ordinarily,  at  the  end  of  twenty -four  hours,  sometimes  even  after  fifteen  or 
sixteen,  the  fermentative  process  is  well  marked.  The  odor  becomes  ammo- 
niacal,  at  the  same  time  that  it  retains  the  peculiar  smell  of  the  pastel.  The 
bath,  hitherto  of  a  brown  color,  now  assumes  a  decided  yellowish-red  tint.  A 
blue  froth,  which  results  from  the  newly  liberated  indigo  of  the  pastel,  floats  on 
the  liquor  as  a  thick  scum,  being  composed  of  small  blue  bubbles,  which  are 
closely  agglomerated  together.  A  brilliant  pellicle  covers  the  bath,  and  beneath 
we  may  perceive  some  blue  or  almost  black  veins,  owing  to  the  indigo  of  the 
pastel  which  rises  towards  the  surface.  If  the  liquor  be  now  agitated  with  a 
switch,  the  small  quantity  of  indigo  which  is  evolved  floats  to  the  top  of  the  bath. 
On  exposing  a  few  drops  of  this  mixture  to  the  air,  the  golden  yellow  color 
quickly  disappears,  and  is  replaced  by  the  blue  tint  of  the  indigo.  This  phe- 
nomenon is  due  to  the  absorption  of  the  oxygen  of  the  air  by  the  indigogen  from 
the  pastel :  in  this  state  we  might  even  dye  wool  with  it  without  any  further 
addition  of  indigo  ;  but  the  colors  which  it  furnishes  are  devoid  of  brilliancy  and 
vivacity  of  tone,  at  the  same  time  that  the  bath  becomes  quickly  exhausted. 

The  signs  above  described  announce,  in  a  most  indubitable  manner,  that 
fermentation  is  established,  and  that  the  vat  has  now  the  power  of  furnishing  to 
the  indigo  the  hydrogen  which  is  required  to  render  it  soluble,  — .that  contained 
in  the  pastel  having  been  already  taken  up  ;  this,  then,  is  the  proper  moment 
for  adding  the  indigo,  which  should  be  previously  ground  in  a  mill. 

We  stated  above  that  the  liquor  of  the  vat  should  be  previously  charged 
with  a  certain  quantity  of  lime  ;  we  also  find  in  it  ammonia  generated  by  the 
pastel ;  but  a  part  of  these  alkalies  become  saturated  by  the  carbonic  acid  gas 
along  with  the  proper  acids  of  the  madder  and  of  the  weld,  as  well  as  by  the 
lactic  acid  produced  by  the  bran  during  fermentation.  The  ordinary  guide  of 
the  dyer  is  the  odor,  which,  according  to  circumstances;  becomes  more  or  less 
ammoniacal.  The  vat  is  said  to  be  either  soft  or  harsh ;  if  soft,  a  little  more 
lime  should  be  added  to  it.    The  fresh  vat  is  always  soft ;  it  exhales  a  feeble 


72 


NOTES  UPON  INDIGO. 


ammoniacal  odor  accompanied  with  the  peculiar  smell  of  the  pastel ;  we  must, 
therefore,  add  lime  to  it  along  with  the  indigo  ;  we  usually  employ  from  five  to 
six  pounds,  and,  after  having  stirred  the  vat,  it  is  to  he  covered  over.  The 
indigo,  being  incapable  of  solution  except  by  its  combination  with  hydrogen, 
gives  no  sign  of  being  dissolved  until  it  has  remained  a  certain  time  in  the  bath. 
We  may  remark  that  the  hard  indigoes,  as  those  of  Java,  require  at  least  eight 
or  nine  hours,  whilst  those  of  Bengal  do  not  need  more  than  six  hours,  for  their 
solution.  We  should  examine  the  vat  again  three  hours  after  adding  the  indigo. 
We  ordinarily  remark  that  the  odor  is  by  this  time  weakened ;  we  must  now  add 
a  further  quantity  of  lime,  sometimes  less,  but  generally  about  equal  in  amount 
to  the  first  portion  ;  it  is  then  to  be  covered  over  again,  and  set  aside  for  three 
hours. 

After  this  lapse  of  time,  the  bath  will  be  found  covered  with  an  abundant 
froth  and  a  very  marked  copper-colored  pellicle ;  the  veins  which  float  upon  its 
surface  are  larger  and  more  marked  than  they  were  previously  ;  the  liquor 
becomes  of  a  deep  yellowish-red  color.  On  dipping  the  rake  into  the  bath,  and 
allowing  the  liquid  to  run  off  at  the  edge,  its  color,  if  viewed  against  the  light,  is 
of  a  strongly  marked  emerald-green,  which  gradually  disappears,  in  proportion 
as  the  indigo  absorbs  oxygen,  and  leaves  in  its  place  a  mere  drop  rendered 
opaque  by  the  blue  color  of  the  indigo.  The  odor  of  the  vat  at  this  instant  is 
strongly  ammoniacal ;  we  also  find  in  it  the  peculiar  scent  of  the  pastel.  When 
we  discover  a  marked  character  of  this  kind  in  the  newly  formed  vat,  we  may 
without  fear  plunge  in  the  stuff  intended  to  be  dyed  ;  but  the  tints  given  during 
the  first  working  of  the  vat  are  never  so  brilliant  as  those  subsequently  formed  ; 
this  is  owing  to  the  yellow-coloring  matters  of  the  pastel,  which,  aided  by  the 
heat,  become  fixed  on  the  wool  at  the  same  time  as  the  indigo,  and  thus  give  to 
it  a  greenish  tint.  This  accident  is  common  both  with  the  pastel  and  the  woad 
vats ;  it  is,  however,  less  marked  in  the  latter. 

When  the  stuff  or  cloth  has  been  immersed  for  an  hour  in  the  vat  it  should 
be  withdrawn;  it  would,  in  fact,  be  useless  to  leave  it  there  for  a  longer  time, 
inasmuch  as  it  could  absorb  no  more  of  the  coloring  principle.  It  is  therefore 
to  be  taken  from  the  bath  and  hung  up  to  dry,  when  the  indigo,  by  attracting 
oxygen,  will  become  insoluble  and  acquire  a  blue  color.  Then  we  may  replunge 
the  stuff  in  the  vat,  and  the  shade  will  immediately  assume  a  deeper  tint,  owing 
to  renewed  absorption  of  indigo  by  the  wool.  By  repeating  these  operations,  we 
succeed  in  giving  very  deep  shades.  We  must  not,  however,  imagine  that  the 
cloth  seizes  only  on  that  portion  of  indigo  contained  in  the  liquor  required  to 
soak  it.  Far  from  such  being  the  case,  experience  shows  that,  during  its  stay  in 
the  bath,  it  appropriates  to  itself,  within  certain  limits,  a  gradually  increasing 
quantity  of  indigo.  We  have  here,  then,  an  action  of  affinity,  or  perhaps  a 
consequence  of  porosity  on  the  part  of  the  wool  itself. 

Woad  Vat.  —  These  vats  are  extensively  employed  at  Louviers,  and  in  the 
manufactories  of  the  north  of  France.  The  bath  is  prepared  in  the  same  manner 
as  in  the  foregoing  case ;  the  finely  cut  root  is  introduced  into  the  copper  along 
with  2  lbs.  of  pounded  indigo,  9  lbs.  of  madder,  and  15i  lbs.  of  slaked  lime. 
The  liquor  is,  after  the  necessary  ebullition,  poured  upon  the  woad.  This  sub- 
stance contains  but  a  very  small  quantity  of  coloring  principle  ;  we  must,  there- 
fore, add  some  indigo  when  preparing  the  vat,  so  as  to  indicate  the  precise 
instant  when  the  mixture  arrives  at  the  point  of  fermentation  so  necessary  for 
imparting  hydrogen  to  the  coloring  principle,  and  for  rendering  it  soluble.  We 
must  also  use  a  larger  quantity  of  lime,  since  the  woad  contains  no  ammonia 


NOTES  UPON  INDIGO. 


73 


resulting  from  previous  decomposition,  such  as  we  find  to  be  the  case  with  the 
pastel  of  the  south.  When  the  vat  is  in  a  suitable  state  of  fermentation,  a  rusty 
color  becomes  manifest,  in  addition  to  the  signs  already  described  in  speaking 
of  the  pastel  vat ;  besides  the  ammoniacal  odor,  the  bath  always  retains  the 
peculiar  smell  of  the  woad.  The  pounded  indigo  is  now  added,  and  we  proceed, 
in  the  manner  already  detailed,  to  reduce  it  to  a  state  of  solution  fit  for  dyeing. 

The  vats  prepared  by  means  of  pastel  have  greater  durability  than  those 
made  with  the  woad  ;  but  it  is  thought  that  the  colors  given  by  the  latter  are 
more  brilliant  than  those  obtained  from  the  former  dye. 

Modified  Pastel  Vat.  —  This  vat  is  about  7  feet  in  depth,  and  6^  feet  in 
diameter.  It  is  made  of  copper,  and  heated  by  steam.  The  lid  is  composed  of 
three  segments,  each  of  which  is  formed  of  two  planks,  about  an  inch  thick,  and 
strongly  secured  together  by  bolts. 

The  beating  is  performed  in  the  usual  way,  with  sticks  before  the  first  dip- 
ping, after  having  moistened  the  cloth  in  tepid  water.  This  operation  is  not 
subsequently  repeated. 

This  vat  is  prepared  with  13  lbs.  of  indigo,  17J  lbs.  of  madder,  4i  lbs.  of 
bran,  9  lbs.  of  lime,  and  4J-  lbs.  of  potash.  Having  filled  the  vat,  we  heat  it  to 
about  200°  Fah.,  and,  as  soon  as  the  water  is  tepid,  introduce  441  lbs.  of  pastel. 
The  liquor  becomes  of  a  yellowish-brown  color ;  small  bubbles  appear  upon  its 
surface,  ordinarily  at  the  end  of  four  hours  if  the  vat  be  heated  by  steam,  but 
not  until  after  eight  or  twelve  hours  where  heat  is 'applied  by  the  common  fire ; 
in  the  latter  case  the  mixture  should  be  stirred  every  three  hours.  When  the 
liquor  displays  the  signs  of  fermentation,  we  add  the  above-mentioned  ingredi- 
ents, and  cover  the  vat  over ;  it  is  then  to  be  set  aside,  stirring  it  every  three 
hours,  or  oftener  if  the  fermentative  action  be  very  rapid.  Each  time  that  it  is 
stirred  we  are  to  add  from  2  to  4  lbs.  of  lime ;  if  fermentation  proceed  quickly 
we  even  use  more,  but  in  the  contrary  case  less.  After  about  eighteen  hours, 
we  plunge  into  the  vat  three  pieces  of  common  cloth,  measuring  from  twenty  to 
twenty-five  ells  in  length  each ;  when  they  have  received  six  or  seven  turns, 
they  are  to  be  taken  out  again.  The  object  of  this  is  to  remove  the  excess  of 
lime  from  the  bath.  The  vat  is  then  set  aside  for  three  hours,  when  it  is  to  be 
stirred,  and  13  lbs.  of  indigo,  with  2  lbs.  of  madder,  added  to  it.  We  now  again 
apply  heat  to  the  mixture. 

If  the  vat  contains  a  superabundance  of  lime,  it  will  be  unnecessary  to  add 
more  ;  otherwise  we  throw  in  a  further  quantity.  During  the  night  it  should  be 
covered  with  a  cloth,  and  a  workman  left  to  watch  it.  It  is  usually  stirred  once 
before  the  morning;  but  if  it  be  deficient  in  lime,  it  will  require  this  manipula- 
tion to  be  more  frequently  repeated,  and  also  fresh  lime  added  to  it.  On  the 
following  day  the  stirring  should  be  continued  every  three  hours,  and  so  on  for 
the  next  thirty  hours,  taking  care  to  heat  the  vat  from  time  to  time.  On  the 
morning  of  the  fourth  day  the  dyeing  may  be  commenced. 

The  temperature  should  be  maintained  at  a  pretty  uniform  point ;  if  it  be 
too  hot,  the  blue  takes  a  red  reflection,  by  reason  of  the  madder  contained  in  the 
liquid.  A  vat  thus  prepared  will  last  three  months  ;  we  may  even  work  it  for 
double  that  period,  but  after  the  third  month  it  appears  to  lose  some  of  its 
indigo. 

We  maintain  the  power  of  the  vat  by  introducing  every  night  2£  lbs.  of 
madder.  Some  indigo  is  also  added  twice  or  three  times  a  week.  These  ad- 
ditions are  made  in  the  evening.  After  the  former,  the  vat  is  left  at  rest  for 
forty-two  hours  ;  with  the  latter  only  for  twenty-four,  at  the  same  time  observ- 


10 


74 


NOTES  UPON  INDIGO. 


ing  the  precautions  already  indicated.  At  the  end  of  three  months,  or  sooner 
when  we  wish  to  stop  the  working  of  the  vat,  we  exhaust  the  indigo ;  for  this 
purpose  we  continue  to  charge  it  every  night  for  the  space  of  a  month  with  mad- 
der, and  dip  into  it  white  cloths,  or  more  particularly  woollen  tissues,  which 
become  more  or  less  loaded  with  the  indigo.  We  must  continue  this  plan  until 
these  matters  take  up  no  further  color.  The  dippings  are  to  be  performed  twice 
a-day  at  first,  but  once  only  towards  the  termination.  Many  dyers  make  use  of 
this  bath  for  preparing  a  new  vat,  but  it  is  better  to  throw  this  away  and  make 
it  up  afresh  with  common  water. 

Indian  Vat.  —  These  vats  are  of  more  simple  and  of  more  ready  construc- 
tion than  the  pastel  or  woad  vats.  We  are  to  boil  in  water  a  quantity  of  madder 
and  of  bran,  proportioned  to  the  weight  of  indigo  which  we  wish  to  employ. 
After  two  hours'  ebullition,  we  turn  into  this  bath  some  tartar-lees,  which  are 
also  to  be  boiled  for  an  hour  and  a  half  or  two  hours,  so  as  to  charge  the  bath 
with  whatever  soluble  matter  they  may  contain ;  after  this  ebullition  the  bath 
should  be  allowed  to  cool,  and  the  indigo,  which  has  been  previously  ground,  is 
then  to  be  introduced.  Supposing  that  we  wish  to  employ  21  lbs.  of  indigo,  the 
following  would  be  the  proportions  used  in  preparing  this  vat :  41  lbs.  tartar  lees, 
13  lbs.  of  madder,  and  5  lbs.  of  bran.  These  vats  are  usually  mounted  in  coppers  of 
a  conical  shape  ;  a  small  fire  should  be  kept  up  around  them,  so  as  to  maintain 
a  moderate  and  uniform  heat.  The  indigo  will  usually  be  found  dissolved  at  the 
end  of  twenty -four  hours,  often  even  after  twelve  or  fifteen  hours.  The  liquor 
has  a  reddish  color  in  the  new  vats,  and  a  green  tint  in  those  which  are  in  a 
working  state.  The  frothy  surface,  as  well  as  the  brilliant-colored  pellicle, 
becomes  manifested  in  this  as  in  all  other  preparations  of  a  like  kind. 

This  species  of  vat  has  to  be  renewed  much  more  frequently  than  the  woad 
and  pastel  vats,  from  the  indigo  being  more  difficult  to  dissolve  after  a  certain 
lapse  of  time.'   A  moderate  heat  should  be  maintained  in  all  these  vats. 

Potash  Vat.  —  This  species  of  vat  is  extensively  employed  at  Elboeuf  for 
the  dyeing  of  wool  in  the  flock.  It  presents  in  all  respects  a  perfect  analogy 
with  the  Indian  vat ;  in  fact,  the  action  of  the  tartar-lee  in  the  latter  preparation 
depends  entirely  on  the  carbonate  of  potash  which  it  contains.  The  ingredients 
used  in  the  preparation  of  the  potash  vat  are  bran,  madder,  and  the  subcar- 
bonate  of  potash  of  commerce. 

We  obtain  the  deep  shades  in  this  species  of  vat  with  greater  celerity  than 
in  all  others,  a  fact  which  undoubtedly  depends  on  the  greater  power  which 
potash  has  of  dissolving  indigo  than  is  possessed  by  lime.  Experience  proves  that 
the  potash  vat  has  the  advantage  in  point  of  celerity  of  nearly  a  third  ;  but  this 
is  balanced  by  the  inconvenience  resulting  from  the  darker  shade,  which  we 
must  attribute  to  the  large  quantity  of  coloring  matter  of  the  madder  dissolved 
by  the  alkaline  lee,  and  which  becomes  fixed  on  the  stuff  with  the  indigo. 

To  render  this  vat  in  its  most  favorable  state,  the  indigo  should  be  made  to 
undergo  a  commencement  of  hydrogenation  before  turning  it  into  the  mixture ; 
for  this  purpose  we  prepare  in  a  small  copper  a  bath  analogous  to  that  in  the  vat, 
to  which  the  pounded  indigo  is  added.  This  bath  is  maintained  for  twenty -four 
hours  at  a  moderate  heat,  taking  care  to  stir  it  from  time  to  time.  The  indigo 
assumes  a  yellowish  color,  becomes  dissolved,  and  in  this  state  is  turned  into  the 
vat ;  we  thus  avoid  many  delays  and  losses  in  its  preparation,  and  indeed  it 
would  be  desirable  if  a  similar  plan  were  adopted  with  all  these  compounds. 

German  Vat.  —  This  vat  is  of  nearly  similar  dimensions  to  that  used  for  the 
woad,  being  three  times  the  size  of  the  potash  vat.    Its  diameter  is  about  6-J-  feet, 


NOTES  UPON  INDIGO. 


75 


and  its  depth  8£  feet.  Having  filled  the  copper  with  water,  we  are  to  heat  it  to 
200°  Fah. ;  we  then  add  20  pailsful  of  bran,  22  lbs.  of  carbonate  of  soda,  11  lbs- 
of  indigo,  and  5-^  pounds  of  lime,  thoroughly  slaked,  in  powder.  The  mixture  is 
to  be  well  stirred,  and  then  set  aside  for  two  hours  ;  the  workman  should  con- 
tinually watch  the  progress  of  the  fermentation,  moderating  it  more  or  less  by 
means  of  lime  or  carbonate  of  soda,  so  as  to  render  the  vat  in  a  working  state  at 
the  end  of  twelve,  fifteen,  or,  at  the  most,  eighteen  hours.  The  odor  is  the  only 
criterion  by  which  the  workman  is  enabled  to  judge  of  the  good  state  of  the  vat, 
he  must  therefore  possess  considerable  tact  and  experience. 

In  the  process  of  dipping  we  introduce  84  lbs.,  106  lbs.,  or  even  130  lbs.  of 
wool,  in  a  net  bag,  similar  to  that  used  in  the  woad  vat,  taking  care  that  the  bag 
is  not  allowed  to  rest  against  the  sides  of  the  copper.  When  the  wool  has 
sufficiently  imbibed  the  color,  we  remove  the  bag  containing  it,  and  allow  it  to 
drain  for  a  short  time  over  the  vessel.  We  operate  in  this  way  on  two  or  three 
quantities  in  succession  ;  we  then  remove  the  vat,  and  set  it  aside  for  two  hours ;  we 
must  be  careful,  from  time  to  time,  to  replace  the  indigo  absorbed  by  the  wool, 
as  also  to  add  fresh  quantities  of  bran,  lime,  and  crystallized  carbonate  of  soda, 
so  as  constantly  to  maintain  the  fermentation  at  a  suitable  point. 

The  German  vat  differs,  then,  from  the  potash  vat  by  the  fact  that  the  potash 
is  replaced  by  crystallized  carbonate  of  soda  and  caustic  lime,  which  latter  sub- 
stance also  gives  to  the  carbonate  of  soda  a  caustic  character.  It  presents  a 
remarkable  saving  as  compared  to  the  potash  vat ;  hence  the  frequency  of  its 
employment ;  but  it  requires  great  care,  and  is  more  difficult  to  manage.  It  also 
offers  considerable  economy  of  labor ;  one  man  is  amply  sufficient  for  each  vat. 

The  army  cloth  is  usually  dyed  by  means  of  the  pastel  vat,  which  gives  the 
most  advantageous  results.  We  here  make  use  of  vats  about  8-J-  feet  in  depth, 
and  5  feet  in  diameter,  into  which  we  introduce  from  361  lbs.  to  405  lbs  of  pastel 
or  of  woad,  after  previous  maceration.  The  vat  is  to  be  filled  with  boiling  water, 
and  we  then  add  to  the  bath  22  lbs.  of  madder,  17-J  lbs.  of  weld,  and  13  lbs.  of 
bran.  The  mixture  is  to  maintained  in  a  state  of  ebullition  for  about  half  an 
hour ;  we  next  add  a  few  pailsful  of  cold  water,  taking  care,  however,  not  to 
lower  the  temperature  beyond  130°  Fah. ;  during  the  whole  of  this  time  a  work- 
man, provided  with  a  rake,  keeps  incessantly  stirring  the  materials  of  the  bath. 
The  vat  is  then  accurately  closed  by  means  of  a  wooden  lid,  and  surrounded  by 
blankets,  so  as  to  keep  up  the  heat.  It  is  now  put  aside  for  six  hours ;  after 
this  time  it  is  again  stirred  by  means  of  a  rake,  for  the  space  of  half  an  hour; 
and  this  operation  should  be  repeated  every  three  hours  until  the  surface  of  the 
bath  becomes  marked  with  blue  veins  ;  we  then  add  from  six  to  eight  pounds  of 
slaked  lime. 

The  color  of  the  vat  now  borders  on  a  blackish-blue.  We  immediately  add 
the  indigo  in  a  quantity  proportioned  to  the  shade  which  we  wish  to  obtain. 
The  pastel  in  the  foregoing  mixture  may  last  for  several  months  ;  but  we  must 
renew  the  indigo  in  proportion  as  it  becomes  exhausted,  at  the  same  time  adding 
both  bran  and  madder.    In  general  we  employ  — 

11  to  13  lbs.  of  good  indigo  for  100  lbs.  of  fine  wool. 

9  to  11  lbs.  of  good  indigo  for  100  lbs.  of  common  wool. 

9  to  11  lbs.  of  good  indigo  for  131  yards  of  cloth  dyed  in  the  piece. 

Management  of  the  Vats. — -A  good  condition  of  the  vat  is  recognized  by 
the  following  characters  :  The  tint  of  the  bath  is  of  a  fine  golden-yellow,  and  its 
surface  is  covered  with  a  bluish  froth  and  a  copper-colored  pellicle.  On  dipping  the 
rake  into  the  bath,  there  escapes  bubbles  of  air,  which  should  burst  very  slowly ; 


76 


NOTES  UPON  INDIGO. 


when  they  vanish  quickly,  it  becomes  an  indication  that  we  must  add  more  lime. 
The  paste  which  is  found  at  the  bottom  of  the  vat,  green  at  the  moment  of  its 
being  drawn  up,  should  become  brown  in  .the  air  ;  if,  however,  it  remains  green, 
this  is  a  further  sign  that  more  lime  is  required.  Lastly,  the  vat  should  exhale 
the  odor  of  indigo.  We  usually  complete  the  assurance  of  the  vat  being  in  a 
good  state  by  plunging  into  it,  after  two  hours'  respite,  a  skein  of  wool,  which, 
on  being  withdrawn  after  the  lapse  of  half  an  hour,  should  present  a  green  color, 
but  change  directly  to  blue.  We  then  once  more  mix  the  materials  of  the  vat, 
and  two  hours  after  it  may  be  considered  ready  for  dyeing. 

These  vats,  like  those  already  described,  are  provided  with  a  large  wooden 
ring,  the  interior  of  wiiich  is  armed  with  a  kind  of  network,  for  the  purpose  of 
preventing  the  objects  which  are  intended  to  be  dyed  coming  in  contact  with  the 
materials  at  the  bottom  of  the  vat ;  we,  moreover,  take  the  precaution  of  enclos- 
ing the  wool  or  cloth  in  bags.  These  tissues,  when  plunged  into  the  bath, 
should  remain  there  for  a  longer  or  shorter  time,  according  to  the  shade  which 
we  wish  to  obtain;  one  dipping,  however,  will  never  suffice  for  this  object; 
usually  we  leave  in  the  stuff  for  half  an  hour  only  ;  it  is  then  to  be  taken  from  the 
bath,  wrung,  and  exposed  to  the  air.  This  operation  is  repeated  until  we  have 
succeeded  in  procuring  the  desired  shade ;  we  ordinarily  suffer  three  hours  to 
elapse  between  each  dipping.  The  heat  of  the  vat  should  never  be  allowed  to 
fall  below  130°  Fah.  After  each  operation  the  bath  must  be  well  stirred,  and. 
fresh  lime  added  ;  generally  speaking,  a  pound  a  day  will  suffice.  We  re-estab- 
lish the  indigo  about  every  second  day.  When  once  this  vat  is  well  mounted, 
and  we  are  careful  to  examine  its  working,  we  may  dye  from  two  to  four  batches 
a  day  with  it. 

When  the  stuffs  have  acquired  the  desired  shade,  they  are  first  to  be  washed 
in  common  water,  and  then  in  a  very  weak  solution  of  hydrochloric  acid  (about 
one  part  in  a  thousand) ;  after  this  they  are  again  rinsed  in  pure  water. 

The  Indian  vat  is  much  more  easily  managed  than  the  foregoing  ;  it  presents 
less  danger  of  failure,  from  the  fact  that  it  is  quickly  exhausted,  and  also  from 
the  fermentative  process,  which  is  so  difficult  to  govern  in  the  pastel  vat ;  this 
vat  not  having  time  to  change  in  character.  It  is  prepared  by  first  introducing 
an  equal  quantity  of  madder  and  of  bran,  and  a  triple  quantity  of  potash  ;  this 
is  to  be  gradually  heated  until  it  reaches  a  temperature  of  167°  Fah.,  and  we 
then  add  to  it  the  indigo,  thoroughly  agitating  the  matters  for  half  an  hour. 
The  vat  is  maintained  at  a  temperature  of  86°  to  100°  Fah.,  by  keeping  it. 
closely  covered,  and  at  the  same  time  the  mixture  is  to  be  stirred  occasionally 
at  intervals  of  twelve  hours.  It  should  by  this  time  present  a  beautiful  green 
shade,  the  liquor  being  surmounted  by  a  copper-colored  pellicle  and  a  purplish 
froth.  We  may  now  commence  the  dyeing,  following  the  same  course  as  with  the 
pastel  vat ;  but  the  stirrings  being  here  repeated  much  more  frequently  than 
with  the  other  mixture,  we  can  dye  a  larger  quantity  of  wool  within  a  given  time. 
When  the  vat  ceases  to  give  a  brilliant  blue,  we  must  altogether  renew  it;  if  it 
be  merely  weakened,  we  add  to  it  a  small  quantity  of  freshly  prepared  liquor 
containing  a  few  pounds  of  potash,  and  a  little  less  bran  and  madder.  In  giving 
the  dark  and  the  clear  sky-blues,  we  must  be  careful  to  employ  a  quantity  of 
indigo  proportioned  to  the  color  which  we  wish  to  obtain,  or,  better  still,  we  may 
use  the  previously  exhausted  vat  for  the  dark  blue. 

When  exposed  to  the  influence  of  the  putrid  fermentation,  indigo  is  decom- 
posed and  loses  its  color.  If  rendered  soluble,  it  obeys  the  impulse  communicated 
to  the  azotized  matters  with  which  it  is  brought  into  contact,  although,  if 


NOTES  UPON  INDIGO. 


77 


macerated  in  pure  water  at  the  ordinary  temperature,  it  is  itself  decomposed 
with  great  difficulty. 

The  pastel  and  the  woad  are  very  prone  to  the  putrid  fermentation,  by 
reason  of  the  large  quantity  of  azotized  matters  which  they  contain,  as  do  all  the 
cruciferae ;  they  require  therefore  considerable  care  in  their  employment. 

When  a  vat  is  mounted,  if  the  fermentation  be  allowed  to  continue  unchecked, 
after  the  appearance  of  the  blue  froth  and  the  other  signs  already  indicated,  the 
liquor  will  acquire  a  yellow  color  similar  to  that  of  beer ;  the  froth  will  become 
white  ;  it  will  give  out  a  stale  smell  and  lose  its  ammoniacal  odor  ;  after  a  few 
days  it  will  turn  whitish,  and  exhale  a  smell  at  first  similar  to  that  of  putre- 
fied animal  substances ;  then  it  will  acquire  the  odor  of  rotten  eggs,  and  set 
free  sulphuretted  hydrogen.  The  lime  in  the  pastel  and  the  woad  vats,  and  the 
tartar-lee  and  potash  in  the  other  mixtures,  are  used  for  the  purpose  of  preventing 
these  accidents. 

Besides  the  oxygenated  compound,  which  is  formed  by  the  combination  of 
oxygen  with  the  extractive  matters  of  the  plants  held  in  digestion,  there  is  a 
production  of  carbonic  acid  which  saturates  the  alkaline  lee,  and  forms  a  carbon- 
ate of  lime  in  the  pastel  vat.  We  find  this  attached  to  the  sides  of  the  vat  in 
such  quantity  that  the  inside  of  these  vessels  becomes  incrusted  with  it  to  a 
considerable  depth.  It  is  this  product  which  dyers  call  the  tartar  of  the  vat ;  it 
effervesces  with  acids,  and  gives  on  analysis  carbonic  acid,  lime,  and  a  few 
particles  of  indigo.  In  the  potash  vat  the  solubility  of  the  carbonate  of  potash 
prevents  its  deposition ;  but  it  is  very  probable  that  we  have  even  here  a  formation 
of  some  carbonated  products,  perhaps  in  part  formed  at  the  expense  of  the 
carbonic  acid  of  the  air. 

The  soluble  extractive  principle  being  the  only  matter  which  remains  in 
solution  in  the  bath  with  the  indigo,  the  lime,  &c,  we  have  formed  deposits  which, 
varying  both  in  their  volume  and  in  the  greater  or  less  facility  with  which  they 
are  precipitated  during  the  various  periods  of  fermentation,  lead  to  a  more  or 
less  considerable  waste  of  time.  If  we  plunge  a  piece  of  woollen  tissue  into  a  vat 
which  has  been  recently  stirred,  it  will  acquire  a  dark  color,  and  will  be  found 
covered  with  brown  stains  which  are  with  difficulty  removed.  When  the  woad 
or  paste  vat  has  been  stirred,  it  need  be  left  two  or  three  hours  only  before 
plunging  in  the  stuff,  at  least  during  the  early  months  of  its  working,  inasmuch 
as  the  pastel,  being  but  slightly  divided  and  attenuated,  is  readily  precipitated  ; 
but  when,  by  reason  of  its  extreme  division,  in  consequence  of  repeated  operations, 
it  is  thrown  down  with  less  facility,  the  dipping  should  not  be  performed  oftener 
than  three  times  in  the  day.      *  | 

The  Indian  vat  requires  less  time  than  the  others  ;  we  may  even  dye  with  it  an 
hour  after  stirring  the  mixture.    The  potash,  being  soluble,  forms  no  precipitate  ;  • 
while  the  ligneous  fibre  of  the  madder  and  the  pellicles  of  the  bran  become  de- 
posited with  great  facility.    We  can  also  dip  with  these  vats  much  oftener  than 
with  those  made  by  pastel  or  woad. 


78 


NOTES  UPON  INDIGO. 


SICKNESS  OF  THE  WARM  VAT  FOR  DYEING  WOOL,  AND  ITS 

REMEDIES. 

We  have  to  thank  that  excellent  practical  magazine,  "  The  Ameri- 
can Chemist,"  for  the  following  notes  on  the  sicknesses  of  the  warm 
vat,  by  F.  W.  Kugler,  translated  from  Reimann's  Farberzeintung :  — 

In  the  wool  indigo  vat,  among  the  principal  "  sicknesses  "  is  the  blackening  of 
the  vat,  or  "  sharpening."  This  arises  from  the  presence  of  too  much  lime. 
When  "  sharpened,"  the  liquor,  instead  of  having  a  waxy  yellow  color  with  a 
dense  blue  film  on  its  surface,  has  no  film ;  while  the  liquor  is  a  dark  blackish- 
green,  and  on  being  stirred  shows  a  gray  or  white  scum  on  its  surface,  while  it 
emits  at  the  same  time  a  pungent  odor.  If  the  vat  is  only  slightly  affected,  it  is 
sufficient  to  add  some  bran  and  madder  and  to  let  it  stand  over  night.  If  it  has 
not  quite  recovered  by  morning,  it  may  be  necessary  to  heat  it  up,  agitate  it,  and 
let  it  stand  for  a  couple  of  hours,  after  which  perhaps  the  addition  of  a  little  lime 
will  be  necessary. 

If  the  vat  is  much  sharpened,  it  is  recommended  to  sink  in  it  a  bag  of  bran, 
and  leave  it  over  night,  when  the  fermentation  will  have  restored  the  vat  in  a 
considerable  degree ;  but  it  will  be  necessary  to  add  lime  cautiously  and  by 
degrees,  to  bring  it  to  a  proper  state  for  working. 

The  theory  of  the  souring  of  the  vat  is  given.  Butyric  fermentation  takes  place 
under  certain  circumstances,  butyric  acid  being  formed ;  and  hydrogen  is  set  free, 
which  reduces  the  indigo.  The  addition  of  lime  makes  the  vat  too  strongly 
alkaline,  and  sets  ammonia  free,  which  gives  the  pungent  odor  of  the  soured 
(verschaften)  vat.  Simultaneously  the  lime  with  the  white  indigo  forms  a 
difficultly  soluble  compound,  which  settles,  and  thus  interferes  with  the  working 
of  the  vat.  The  excess  of  lime  must  be  removed,  which  is  accomplished  by 
introducing  bran,  which  causes  a  lactic  fermentation  ;  and  the  lactic  acid  neutral- 
izes the  excess  of  lime,  and  destroys  the  lime  compound  with  indigo  which  had 
been  formed.  The  lime  may  be  neutralized  by  the  use  of  mineral  acids,  but 
there  is  danger  in  that  case  of  precipitating  the  indigo. 

A  second  "  sickness  "  is  "  becoming  too  sweet."  The  symptoms  are,  —  the  blue 
veins  and  surface  film  disappear  on  stirring,  the  foam  gives  a  rustling  sound,  the 
bath  assumes  a  reddish-yellow  color,  blue  goods  placed  in  the  bath  lose  their 
color;  and  the  vat  has  an  unpleasant  odor. 

The  vat  when  "too  sweet"  needs  to  be  brought  to  the  regular  temperature, 
and  lime  to  be  added  cautiously  until  the  vat  is  brought  to  its  normal  state.  It 
is  safer  to  add  an  excess  of  lime  and  "  sour  "  the  vat,  and  then  bring  it  back 
according  to  the  directions  under  that  head,  than  to  add  too  little,  as  less  indigo 
is  lost.  To  use  up  all  the  dye  and  to  dye  a  light  blue,  as  little  lime  should  be 
present  as  is  consistent  with  the  workings  of  the  vat. 

The  cause  of  the  "  falling  away  "  of  the  vat  is  a  too  active  fermentation,  which 
produces  considerable  lactic  acid,  from  which  butyric  acid  forms,  setting  free 
hydrogen,  thereby  making  white  indigo,  which,  if  the  action  is  allowed  to  continue, 
changes  to  a  compound  from  which  the  indigo  cannot  be  recovered.  If  lime  is 
added,  the  lactic  and  butyric  acids  unite  with  it  and  precipitate  it,  while  the  excess 
precipitates  the  white  indigo,  which  is  slowly  recovered,  as  fermentation  pro- 
gresses, which  forms  lactic  acid,  which,  taking  the  place  of  the  white  indigo,  sets 
it  free.    Besides  the  sicknesses,  there  are  various  results  of  mismanagement,  of 


NOTES  UPON  INDIGO. 


79 


which  the  first  is  overwarming,  which  causes  the  bath  to  turn  brown,  which  is 
the  beginning  of  the  souring. 

When  the  bath  begins  to  sour  from  overheating,  some  logwood  should  be 
added  and  then  bran,  and  the  vat  left  to  itself  over  night.  The  reason  of  it  is 
that  the  temperature  is  too  high  for  the  desired  fermentation  to  operate.  The 
vat  sometimes  suddenly  turns  green,  and  even  when  indigo  and  the  other 
necessary  ingredients  are  added  it  remains  of  this  color.  This  is  called  the 
"  breaking  up  of  the  vat."  The  reason  is  that  the  temperature  is  too  low  ;  to 
remedy  it,  it  is  necessary  to  add  logwood  and  bran,  warm  it  up,  and  stir,  when  it 
should  stand  for  some  hours. 


9 


GETTY  CENTER  LIBRARY 


